asm.pdf

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Overview of Automatic Storage Management (ASM)

Automatic Storage Management (ASM) simplifies administration of Oracle related files by allowing

the administrator to reference disk groups rather than individual disks and files, which are managed by

ASM. The ASM functionality is an extention of the Oracle Managed Files (OMF) functionality that

also includes striping and mirroring to provide balanced and secure storage. The new ASM

functionality can be used in combination with existing raw and cooked file systems, along with OMF

and manually managed files.

The ASM functionality is controlled by an ASM instance. This is not a full database instance, just the

memory structures and as such is very small and lightweight.

The main components of ASM are disk groups, each of which comprise of several physical disks that

are controlled as a single unit. The physical disks are known as ASM disks, while the files that reside

on the disks are know as ASM files. The locations and names for the files are controlled by ASM, but

user-friendly aliases and directory structures can be defined for ease of reference.

The level of redundancy and the granularity of the striping can be controlled using templates. Default

templates are provided for each file type stored by ASM, but additional templates can be defined as

needed.

Failure groups are defined within a disk group to support the required level of redundancy. For two-

way mirroring you would expect a disk group to contain two failure groups so individual files are

written to two locations.

In summary ASM provides the following functionality:

Manages groups of disks, called disk groups.

Manages disk redundancy within a disk group.

Provides near-optimal I/O balancing without any manual tuning.

Enables management of database objects without specifying mount points and filenames.

Supports large files.

It is worth taking a quick look at the following section of the documentation to familiarize yourself

with the basic requirements recommendations for ASM.

What are the file types that ASM support and keep in disk groups?

Control files

Flashback logs

Data Pump dump sets

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Data files

DB SPFILE

Data Guard configuration

Temporary data files

RMAN backup sets

Change tracking bitmaps

Online redo logs

RMAN data file copies

OCR files

Archive logs

Transport data files

ASM SPFILE

Can my RDBMS and ASM instances run different versions?

Yes. ASM can be at a higher version or at lower version than its client databases. There’s two

components of compatiblity:

Software compatibility

Diskgroup compatibility attributes:

compatible.asm

compatible.rdbms

Initialization Parameters and ASM Instance Creation

The initialization parameters that are of specific interest for an ASM instance are:

INSTANCE_TYPE - Set to ASM or RDBMS depending on the instance type. The default is

RDBMS.

DB_UNIQUE_NAME - Specifies a globally unique name for the database. This defaults to +ASM

but must be altered if you intend to run multiple ASM instances.

ASM_POWER_LIMIT -The maximum power for a rebalancing operation on an ASM instance.

The valid values range from 1 to 11, with 1 being the default. The higher the limit the more resources

are allocated resulting in faster rebalancing operations. This value is also used as the default when the

POWER clause is omitted from a rebalance operation.

ASM_DISKGROUPS - The list of disk groups that should be mounted by an ASM instance during

instance startup, or by the ALTER DISKGROUP ALL MOUNT statement. ASM configuration changes are

automatically reflected in this parameter.

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ASM_DISKSTRING - Specifies a value that can be used to limit the disks considered for

discovery. Altering the default value may improve the speed of disk group mount time and the speed of

adding a disk to a disk group. Changing the parameter to a value which prevents the discovery of

already mounted disks results in an error. The default value is NULL allowing all suitable disks to be

considered.

Incorrect usage of parameters in ASM or RDBMS instances result in ORA-15021 errors.

To create an ASM instance first create a file called "init+ASM.ora" in the "/tmp" directory containing

the following information.

INSTANCE_TYPE=ASM

Next, using SQL*Plus connect to the ide instance.

export ORACLE_SID=+ASM

sqlplus / as sysdba

Create an spfile using the contents of the "init+ASM.ora" file.

SQL> CREATE SPFILE FROM PFILE='/tmp/init+ASM.ora';

File created.

Finally, start the instance with the NOMOUNT option.

SQL> startup nomount

ASM instance started

Total System Global Area 125829120 bytes

Fixed Size 1301456 bytes

Variable Size 124527664 bytes

Database Buffers 0 bytes

Redo Buffers 0 bytes

SQL>

The ASM instance is now ready to use for creating and mounting disk groups. To shutdown the ASM

instance issue the following command.

SQL> shutdown

ASM instance shutdown

SQL>

Once an ASM instance is present disk groups can be used for the following parameters in database

instances (INSTANCE_TYPE=RDBMS) to allow ASM file creation:

DB_CREATE_FILE_DEST DB_CREATE_ONLINE_LOG_DEST_n

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DB_RECOVERY_FILE_DEST CONTROL_FILES LOG_ARCHIVE_DEST_n LOG_ARCHIVE_DEST STANDBY_ARCHIVE_DEST

Startup and Shutdown of ASM Instances

ASM instance are started and stopped in a similar way to normal database instances. The options for

the STARTUP command are:

FORCE - Performs a SHUTDOWN ABORT before restarting the ASM instance.

MOUNT - Starts the ASM instance and mounts the disk groups specified by the

ASM_DISKGROUPS parameter.

NOMOUNT - Starts the ASM instance without mounting any disk groups.

OPEN - This is not a valid option for an ASM instance.

The options for the SHUTDOWN command are:

NORMAL - The ASM instance waits for all connected ASM instances and SQL sessions to exit

then shuts down.

IMMEDIATE - The ASM instance waits for any SQL transactions to complete then shuts down.

It doesn't wait for sessions to exit.

TRANSACTIONAL - Same as IMMEDIATE.

ABORT - The ASM instance shuts down instantly.

ASM Stripping

ASM stripes files across all the disks within the disk group thus increasing performance, each

stripe is called an ‘allocation unit’. ASM offers two types of stripping which is dependent on

the type of database file

Coarse Stripping used for datafile, archive logs (1MB stripes)

Fine Stripping used for online redo logs, controlfile, flashback files(128KB stripes)

ASM Mirroring

Disk mirroring provides data redundancy, this means that if a disk were to fail Oracle will

use the other mirrored disk and would continue as normal. Oracle mirrors at the extent level,

so you have a primary extent and a mirrored extent. When a disk fails, ASM rebuilds the

failed disk using mirrored extents from the other disks within the group, this may have a

slight impact on performance as the rebuild takes place.

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All disks that share a common controller are in what is called a failure group, you can ensure

redundancy by mirroring disks on separate failure groups which in turn are on different

controllers, ASM will ensure that the primary extent and the mirrored extent are not in the

same failure group. When mirroring you must define failure groups otherwise the mirroring

will not take place.

Administering ASM Disk Groups

There are a few basic points to consider when planning to use ASM:

In most cases you will only need two disk groups (DATA and FRA), where DATA holds all

database related files and FRA holds the fast recovery area, including multiplexed copies on online

redo logs and controlfiles. Typically, the FRA disk group will be twice the size of the DATA disk

group, since it must hold all backups.

Oracle recommend a minimum of 4 LUNs per disk group, with LUNs using hardware RAID

and external redundancy if possible.

All LUNs within a disk group should be the same size and have the same performance

characteristics.

LUNs should be made up from disks dedicated to Oracle, not shared with other applications.

Now let's look at basic administration of disk groups.

Disks

Disk groups are created using the CREATE DISKGROUP statement. This statement allows you to specify

the level of redundancy:

NORMAL REDUNDANCY - Two-way mirroring, requiring two failure groups.

HIGH REDUNDANCY - Three-way mirroring, requiring three failure groups.

EXTERNAL REDUNDANCY - No mirroring for disks that are already protected using hardware

mirroring or RAID. If you have hardware RAID it should be used in preference to ASM redundancy, so

this will be the standard option for most installations.

In addition failure groups and preferred names for disks can be defined. If the NAME clause is omitted

the disks are given a system generated name like "disk_group_1_0001". The FORCE option can be used

to move a disk from another disk group into this one.

CREATE DISKGROUP disk_group_1 NORMAL REDUNDANCY

FAILGROUP failure_group_1 DISK

'/devices/diska1' NAME diska1,

'/devices/diska2' NAME diska2

FAILGROUP failure_group_2 DISK

'/devices/diskb1' NAME diskb1,

'/devices/diskb2' NAME diskb2;

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Disk groups can be deleted using the DROP DISKGROUP statement.

DROP DISKGROUP disk_group_1 INCLUDING CONTENTS;

Disks can be added or removed from disk groups using the ALTER DISKGROUP statement. Remember

that the wildcard "*" can be used to reference disks so long as the resulting string does not match a disk

already used by an existing disk group.

-- Add disks.

ALTER DISKGROUP disk_group_1 ADD DISK

'/devices/disk*3',

'/devices/disk*4';

-- Drop a disk.

ALTER DISKGROUP disk_group_1 DROP DISK diska2;

Disks can be resized using the RESIZE clause of the ALTER DISKGROUP statement. The statement can be

used to resize individual disks, all disks in a failure group or all disks in the disk group. If the SIZE

clause is omitted the disks are resized to the size of the disk returned by the OS.

-- Resize a specific disk.

ALTER DISKGROUP disk_group_1

RESIZE DISK diska1 SIZE 100G;

-- Resize all disks in a failure group.


RESIZE DISKS IN FAILGROUP failure_group_1 SIZE 100G;

-- Resize all disks in a disk group.


RESIZE ALL SIZE 100G;

The UNDROP DISKS clause of the ALTER DISKGROUP statement allows pending disk drops to be undone.

It will not revert drops that have completed, or disk drops associated with the dropping of a disk group.

ALTER DISKGROUP disk_group_1 UNDROP DISKS;

Disk groups can be rebalanced manually using the REBALANCE clause of the ALTER DISKGROUP

statement. If the POWER clause is omitted the ASM_POWER_LIMIT parameter value is used. Rebalancing is

only needed when the speed of the automatic rebalancing is not appropriate.

ALTER DISKGROUP disk_group_1 REBALANCE POWER 5;

Disk groups are mounted at ASM instance startup and unmounted at ASM instance shutdown. Manual

mounting and dismounting can be accomplished using the ALTER DISKGROUP statement as seen below.

ALTER DISKGROUP ALL DISMOUNT;

ALTER DISKGROUP ALL MOUNT;

ALTER DISKGROUP disk_group_1 DISMOUNT;

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ALTER DISKGROUP disk_group_1 MOUNT;

Templates

Templates are named groups of attributes that can be applied to the files within a disk group. The

following example show how templates can be created, altered and dropped.

-- Create a new template.

ALTER DISKGROUP disk_group_1 ADD TEMPLATE my_template ATTRIBUTES (MIRROR FINE);

-- Modify template.

ALTER DISKGROUP disk_group_1 ALTER TEMPLATE my_template ATTRIBUTES (COARSE);

-- Drop template.

ALTER DISKGROUP disk_group_1 DROP TEMPLATE my_template;

Available attributes include:

UNPROTECTED - No mirroring or striping regardless of the redundancy setting.

MIRROR - Two-way mirroring for normal redundancy and three-way mirroring for high

redundancy. This attribute cannot be set for external redundancy.

COARSE - Specifies lower granuality for striping. This attribute cannot be set for external

redundancy.

FINE - Specifies higher granularity for striping. This attribute cannot be set for external

redundancy.

Directories

A directory heirarchy can be defined using the ALTER DISKGROUP statement to support ASM file

aliasing. The following examples show how ASM directories can be created, modified and deleted.

-- Create a directory.

ALTER DISKGROUP disk_group_1 ADD DIRECTORY '+disk_group_1/my_dir';

-- Rename a directory.

ALTER DISKGROUP disk_group_1 RENAME DIRECTORY '+disk_group_1/my_dir' TO

'+disk_group_1/my_dir_2';

-- Delete a directory and all its contents.

ALTER DISKGROUP disk_group_1 DROP DIRECTORY '+disk_group_1/my_dir_2' FORCE;

Aliases

Aliases allow you to reference ASM files using user-friendly names, rather than the fully qualified

ASM filenames.

-- Create an alias using the fully qualified filename.

ALTER DISKGROUP disk_group_1 ADD ALIAS '+disk_group_1/my_dir/my_file.dbf'

FOR '+disk_group_1/mydb/datafile/my_ts.342.3';

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-- Create an alias using the numeric form filename.

ALTER DISKGROUP disk_group_1 ADD ALIAS '+disk_group_1/my_dir/my_file.dbf'

FOR '+disk_group_1.342.3';

-- Rename an alias.

ALTER DISKGROUP disk_group_1 RENAME ALIAS '+disk_group_1/my_dir/my_file.dbf'

TO '+disk_group_1/my_dir/my_file2.dbf';

-- Delete an alias.

ALTER DISKGROUP disk_group_1 DELETE ALIAS '+disk_group_1/my_dir/my_file.dbf';

Attempting to drop a system alias results in an error.

Files

Files are not deleted automatically if they are created using aliases, as they are not Oracle Managed

Files (OMF), or if a recovery is done to a point-in-time before the file was created. For these

circumstances it is necessary to manually delete the files, as shown below.

-- Drop file using an alias.

ALTER DISKGROUP disk_group_1 DROP FILE '+disk_group_1/my_dir/my_file.dbf';

-- Drop file using a numeric form filename.

ALTER DISKGROUP disk_group_1 DROP FILE '+disk_group_1.342.3';

-- Drop file using a fully qualified filename.

ALTER DISKGROUP disk_group_1 DROP FILE '+disk_group_1/mydb/datafile/my_ts.342.3';

Checking Metadata

The internal consistency of disk group metadata can be checked in a number of ways using the CHECK

clause of the ALTER DISKGROUP statement.

-- Check metadata for a specific file.

ALTER DISKGROUP disk_group_1 CHECK FILE '+disk_group_1/my_dir/my_file.dbf'

-- Check metadata for a specific failure group in the disk group.

ALTER DISKGROUP disk_group_1 CHECK FAILGROUP failure_group_1;

-- Check metadata for a specific disk in the disk group.

ALTER DISKGROUP disk_group_1 CHECK DISK diska1;

-- Check metadata for all disks in the disk group.

ALTER DISKGROUP disk_group_1 CHECK ALL;

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ASM Views

The ASM configuration can be viewed using the V$ASM_% views, which often contain different

information depending on whether they are queried from the ASM instance, or a dependant db instance.

View ASM Instance DB Instance

V$ASM_ALIAS Displays a row for each alias present in every

disk group mounted by the ASM instance. Returns no rows

V$ASM_CLIENT Displays a row for each database instance

using a disk group managed by the ASM

instance.

Displays a row for the ASM instance if the database has

open ASM files.

V$ASM_DISK Displays a row for each disk discovered by

the ASM instance, including disks which are

not part of any disk group.

Displays a row for each disk in disk groups in use by

the database instance.

V$ASM_DISKGROUP Displays a row for each disk group

discovered by the ASM instance.

Displays a row for each disk group mounted by the

local ASM instance.

V$ASM_FILE Displays a row for each file for each disk

group mounted by the ASM instance. Displays no rows.

V$ASM_OPERATION Displays a row for each file for each long

running operation executing in the ASM

instance.

Displays no rows.

V$ASM_TEMPLATE Displays a row for each template present in

each disk group mounted by the ASM

instance.

Displays a row for each template present in each disk

group mounted by the ASM instance with which the

database instance communicates.

ASM Filenames

There are several ways to reference ASM file. Some forms are used during creation and some for

referencing ASM files. The forms for file creation are incomplete, relying on ASM to create the fully

qualified name, which can be retrieved from the supporting views. The forms of the ASM filenames are

summarised below.

Filename Type Format

Fully Qualified ASM Filename +dgroup/dbname/file_type/file_type_tag.file.incarnation

Numeric ASM Filename +dgroup.file.incarnation

Alias ASM Filenames +dgroup/directory/filename

Alias ASM Filename with Template +dgroup(template)/alias

Incomplete ASM Filename +dgroup

Incomplete ASM Filename with Template +dgroup(template)

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SQL and ASM

ASM filenames can be used in place of conventional filenames for most Oracle file types, including

controlfiles, datafiles, logfiles etc. For example, the following command creates a new tablespace with

a datafile in the disk_group_1 disk group.

CREATE TABLESPACE my_ts DATAFILE '+disk_group_1' SIZE 100M AUTOEXTEND ON;

New Disk Group Compatibility Attributes

Oracle 11g ASM includes two new compatibility attributes that determine the version of the ASM and

database software that can use specific disk groups:

COMPATIBLE.ASM - The minimum version of the ASM software that can access the disk group.

In 11g, the default setting is 10.1.

COMPATIBLE.RDBMS - The minimum COMPATIBLE database initialization parameter setting for

any database instance that uses the disk group. In 11g, the default setting is 10.1.

The compatibility versions of a disk group can only be increased, not decreased. If you have increased

the version by mistake, you will need to create a new disk group.

The disk group compatibility attributes can be set during disk group creation by adding the ATTRIBUTE

clause to the CREATE DISKGROUP command.

CREATE DISKGROUP data DISK '/dev/raw/*'

ATTRIBUTE 'compatible.asm' = '11.1';

CREATE DISKGROUP data DISK '/dev/raw/*'

ATTRIBUTE 'compatible.rdbms' = '11.1', 'compatible.asm' = '11.1';

The disk group compatibility attributes for existing disk groups can be altered using the SET

ATTRIBUTE clause to the ALTER DISKGROUP command.

ALTER DISKGROUP data SET ATTRIBUTE 'compatible.asm' = '11.1';

ALTER DISKGROUP data SET ATTRIBUTE 'compatible.rdbms' = '11.1';

The current compatibility settings are available from the V$ASM_DISKGROUP and V$ASM_ATTRIBUTE

views.

COLUMN name FORMAT A10

COLUMN compatibility FORMAT A20

COLUMN database_compatibility FORMAT A20

SELECT group_number, name, compatibility, database_compatibility FROM

v$asm_diskgroup;

GROUP_NUMBER NAME COMPATIBILITY DATABASE_COMPATIBILI

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------------ ---------- -------------------- --------------------

1 DATA 11.1.0.0.0 11.1.0.0.0

1 row selected.

SQL>

COLUMN name FORMAT A20

COLUMN value FORMAT A20

SELECT group_number, name, value FROM v$asm_attribute ORDER BY group_number, name;

GROUP_NUMBER NAME VALUE

------------ -------------------- --------------------

1 au_size 1048576

1 compatible.asm 11.1.0.0.0

1 compatible.rdbms 11.1

1 disk_repair_time 3.6h

4 rows selected.

SQL>

Fast Mirror Resync

During transient disk failures within a failure group, ASM keeps track of the changed extents that need

to be applied to the offline disk. Once the disk is available, only the changed extents are written to

resynchronize the disk, rather than overwriting the contents of the entire disk. This can speed up the

resynchronization process considerably.

Fast mirror resync is only available when the disk groups compatibility attributes are set to 11.1 or

higher.

ALTER DISKGROUP disk_group_1 SET ATTRIBUTE 'compatible.asm' = '11.1';

ALTER DISKGROUP disk_group_1 SET ATTRIBUTE 'compatible.rdbms' = '11.1;

ASM drops disks if they remain offline for more than 3.6 hours. The disk groups default time limit is

altered by changing the DISK_REPAIR_TIME parameter with a unit of minutes (M or m) or hours (H or

h).

-- Set using the hours unit of time.

ALTER DISKGROUP disk_group_1 SET ATTRIBUTE 'disk_repair_time' = '4.5h';

-- Set using the minutes unit of time.

ALTER DISKGROUP disk_group_1 SET ATTRIBUTE 'disk_repair_time' = '300m';

The DROP AFTER clause of the ALTER DISKGROUP command is used to override the disk group default

DISK_REPAIR_TIME.

-- Use the default DISK_REPAIR_TIME for the diskgroup.

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ALTER DISKGROUP disk_group_1 OFFLINE DISK D1_0001;

-- Override the default DISK_REPAIR_TIME.

ALTER DISKGROUP disk_group_1 OFFLINE DISK D1_0001 DROP AFTER 30m;

If a disk goes offline during a rolling upgrade, the timer is not started until after the rolling upgrade is

complete.

Rolling Upgrade

Clustered ASM instances for 11g onwards can be upgraded using a rolling upgrade. The ASM cluster is

placed in rolling upgrade mode by issuing the following command from one of the nodes.

ALTER SYSTEM START ROLLING MIGRATION TO 11.2.0.0.0;

Once the cluster is in rolling upgrade mode each node in turn can be shutdown, upgraded and started.

The cluster runs in a mixed version environment until the upgrade is complete. In this state, the cluster

is limited to the following operations:

Mount and dismount of the disk groups.

Open, close, resize, and delete of database files.

Access to local fixed views and fixed packages.

The current status of the ASM cluster can be determined using the following query.

SELECT SYS_CONTEXT('sys_cluster_properties', 'cluster_state') FROM dual;

Once the last node is upgraded, the rolling upgrade is stopped by issuing the following command,

which checks all ASM instances are at the appropriate version, turns off rolling upgrade mode and

restarts any pending rebalance operations.

ALTER SYSTEM STOP ROLLING MIGRATION;

Restrictions and miscellaneous points about the rolling upgrade process include:

The Oracle clusterware must be fully patched before an ASM rolling upgrade is started.

Rolling upgrades are only available from 11g onwards, so this method is not suitable for 10g

to 11g upgrades.

This method can be used to rollback to the previous version if the rolling upgrade fails before

completion.

If the upgrade fails, any rebalancing operations must complete before a new upgrade can be

attempted.

New instances joining the cluster during a rolling upgrade are automatically placed in rolling

upgrade mode.

If all instances in a cluster are stopped during a rolling upgrade, once the instances restart they

will no longer be in rolling upgrade mode. The upgrade must be initiated as if it were a new process.

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SYSASM Privilege and OSASM OS Group

The introduction of ASM moved the management of storage away from system adminstrators and into

the DBA territory. Unfortunately this isn't how every company operates. As a result, some system

administrators were required to have access to privileged users to handle disk storage. Oracle addresses

this issue with the introduction of the SYSASM privilege and the OSASM operating system group,

which provide two mechanisms to enable the separation of storage and database administration duties.

Users can be created in the ASM instance in a similar manner to database users. Granting these users

the SYSASM privilege allows them to connect to the ASM instance and perform administration tasks.

First, connect to the ASM instance.

$ export ORACLE_SID=+ASM

$ sqlplus / as sysasm

Next, create a new user in the ASM instance and grant it the SYSASM privilege. The user is now able

to connect using SYSASM.

SQL> CREATE USER asm_user_1 IDENTIFIED by asm_password;

User created.

SQL> GRANT SYSASM TO asm_user_1;

Grant succeeded.

SQL> CONN asm_user_1/asm_password AS SYSASM

Connected.

SQL>

Alternatively, assigning an operating system user to the OSASM group (asmadmin) allows then to

connect as SYSASM using OS authentication. The following example creates a new OS user assigned

to the OSASM group (asmadmin), which is immediately able to connect using SYSASM.

# useradd tim_hall -G asmadmin

# su - tim_hall

$ export ORACLE_SID=+ASM

$ export ORACLE_HOME=/u01/app/oracle/product/11.1.0/db_1

$ $ORACLE_HOME/bin/sqlplus / as sysasm

SQL*Plus: Release 11.1.0.6.0 - Production on Fri Aug 8 16:48:37 2008

Copyright (c) 1982, 2007, Oracle. All rights reserved.

Connected to:

Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production

With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>

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Scalability and Performance Enhancements

ASM files are stored in a disk group as a collection of extents. In Oracle 10g each extent mapped

directly to one allocation unit (AU), but in Oracle 11g an extent can be made up of one or more

allocation units. As files get larger, the extent size can grow to reduce the size of the extent map

describing the file, thus saving memory.

When the disk group compatibility attributes are set to 11.1 or higher, the extent size will automatically

grow as the file grows. In 11.1, the first 20,000 extents match the allocation unit size (1*AU). The next

20,000 extents are made up of 8 allocation units (8*AU). Beyond that point, the extent size becomes 64

allocation units (64*AU). In 11.2 this behavior has changed from 1, 8, 64 to 1, 4, 16.

In addition to the automatic expansion of the extent sizes, Oracle 11g also allows control over the

allocation unit size using the ATTRIBUTE clause in the CREATE DISKGROUP statement, with values

ranging from 1M to 64M.

CREATE DISKGROUP disk_group_2

EXTERNAL REDUNDANCY

DISK '/dev/sde1'

ATRRIBUTE 'au_size' = '32M';

The combination of expanding extent sizes and larger allocation units should result in increased I/O

performance for very large databases.

New ASMCMD Commands and Options

The ASM command line utility includes several new commands. The following example output

assumes you have already started the utility using the "-p" option.

$ asmcmd -p

ASMCMD [+] >

The usage notes for each command is available by issuing the "help <command>" command from

within the asmcmd utility, so I will avoid displaying all this information here.

The lsdsk command lists information about ASM disks from the V$ASM_DISK_STAT and V$ASM_DISK

views. The summary usage is shown below.

lsdsk [-ksptcgHI] [-d <diskgroup_name>] [pattern]

An example of the output from the basic command and the "-k" option are shown below.

ASMCMD [+] > lsdsk

Path

/dev/sdc1

/dev/sdd1

http://docs.oracle.com/cd/B28359_01/server.111/b31107/asm_util.htm#sthref419

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/dev/sde1

ASMCMD [+] > lsdsk -d data -k

Total_MB Free_MB OS_MB Name Failgroup Library Label UDID Product

Redund Path

8189 6961 8189 DATA_0000 DATA_0000 System

UNKNOWN /dev/sdc1

8189 6961 8189 DATA_0001 DATA_0001 System

UNKNOWN /dev/sdd1

8189 6950 8189 DATA_0002 DATA_0002 System

UNKNOWN /dev/sde1

ASMCMD [+] >

The cp command allows files to be copied between ASM and local or remote destinations. The

summary usage is shown below.

cp [-ifr] <[@connect_identifier:]src> <[@connect_identifier:]tgt>

The following example copies the current USERS datafile from ASM to the local file system.

ASMCMD [+] > cp +DATA/db11g/datafile/users.273.661514191 /tmp/users.dbf

source +DATA/db11g/datafile/users.273.661514191

target /tmp/users.dbf

copying file(s)...

file, /tmp/users.dbf, copy committed.

ASMCMD [+] >

There seems to be some concern that the cp command doesn't work for control files (here).

The md_backup command makes a copy of the metadata for one or more disk groups. The summary

usage is shown below.

md_backup [-b location_of_backup] [-g dgname [-g dgname …]]

An example of the command is shown below. The resulting file contains all the metadata needed to

recreate the ASM setup.

ASMCMD [+] > md_backup -b /tmp/backup.txt -g data

Disk group to be backed up: DATA

ASMCMD [+] >

The md_restore command allows you to restore a disk group from the metadata created by the

md_backup command. It also allows a certain amount of manipulation of the final disk groups during

the restore. The summary usage is shown below.

md_restore -b <backup_file> [-li]

[-t (full)|nodg|newdg] [-f <sql_script_file>]

[-g '<diskgroup_name>,<diskgroup_name>,...']

[-o '<old_diskgroup_name>:<new_diskgroup_name>,...']

A straight restore of the backup shown previously is shown below.


http://www.pythian.com/blogs/910/oracle-asm-11g-does-the-asmcmd-cp-command-really-work



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ASMCMD [+] > md_restore -b /tmp/backup.txt -t full -g data

The remap command repairs a range of physical blocks on disk. The contents of each block is not

validated, so only blocks exhibiting read errors are repaired. The summary usage is shown below.

remap <disk group name> <disk name> <block range>

An example of the command is show below.

ASMCMD [+] > remap data data_0001 5000-5999

For detailed usage information see the ASMCDM Command Reference.

Preferred Read Failure Groups

In Oracle 10g, ASM always reads the primary copy of the mirrored extent set. This isn't a problem

when both nodes and both failure groups are all located in the same site, but it can be inefficient for

extended clusters, causing needless network traffic. Oracle 11g allows each node to define a preferred

failure group, allowing nodes in extended clusters to access local failure groups in preference to remote

ones.

To configure preferred read failure groups the disk group compatibility attributes must be set to 11.1 or

higher. Once the compatibility options are correct, the ASM_PREFERRED_READ_FAILURE_GROUPS

parameter is set to the preferred failure groups for each node.

SELECT name, failgroup FROM v$asm_disk;

NAME FAILGROUP

------------------------------ ------------------------------

DATA_0000 DATA_0000

DATA_0001 DATA_0001

DATA_0002 DATA_0002

3 rows selected.

SQL>

ALTER SYSTEM SET ASM_PREFERRED_READ_FAILURE_GROUPS = 'data.data_0000',

'data.data_0001', 'data.data_0002';

Fast Rebalance

The "ALTER DISKGROUP ... MOUNT" statement allows disk groups to be mounted in restricted mode.

SQL> SELECT name FROM v$asm_diskgroup;

NAME

------------------------------


http://docs.oracle.com/cd/B28359_01/server.111/b31107/asm_util.htm#BABCCEJC

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DATA

SQL> ALTER DISKGROUP data DISMOUNT;

Diskgroup altered.

SQL> ALTER DISKGROUP data MOUNT RESTRICTED;

Diskgroup altered.

SQL> ALTER DISKGROUP data DISMOUNT;

Diskgroup altered.

SQL> ALTER DISKGROUP data MOUNT;

Diskgroup altered.

SQL>

In a RAC environment, a disk group mounted in RESTRICTED mode can only be accessed by a single

instance. The restricted disk group is not available to any ASM clients, even on the node where it is

mounted.

Using RESTRICTED mode improves the performance of rebalance operations in a RAC environment as

it elimitates the need for lock and unlock extent map messaging that occurs between ASM instances.

Once the rebalance operation is complete, the disk group should be dismounted then mounted in

NORMAL mode (the default).

Miscellaneous Disk Group Maintenance Enhancements

The CREATE DISKGROUP and ALTER DISKGROUP commands include a new ATTRIBUTE clause

(compatible, disk_repair_time, au_size).

The CHECK clause of the ALTER DISKGROUP command has been simplified so there are only

two options, NOREPAIR and REPAIR, available, with NOREPAIR as the default. Summarized errors are

displayed, with full error messages writen to the alert log. ALTER DISKGROUP data CHECK; -- Like NOREPAIR

ALTER DISKGROUP data CHECK NOREPAIR;

ALTER DISKGROUP data CHECK REPAIR;

Disk groups can now be mounted in restricted mode, which can improve performance of some

maintenance tasks.

The ALTER DISKGOUP command now includes ONLINE and OFFLINE clauses so disks can be

taken offline for repair before being brought back online. -- Individual disks.

ALTER DISKGROUP data OFFLINE DISK 'disk_0000', 'disk_0001';

ALTER DISKGROUP data ONLINE DISK 'disk_0000', 'disk_0001';

-- Failure groups.

http://www.oracle-base.com/articles/11g/asm-enhancements-11gr1.php#new_disk_group_compatibility_attributes

http://www.oracle-base.com/articles/11g/asm-enhancements-11gr1.php#fast_mirror_resync

http://www.oracle-base.com/articles/11g/asm-enhancements-11gr1.php#scalability_and_performance_enhancements

http://www.oracle-base.com/articles/11g/asm-enhancements-11gr1.php#fast_rebalance

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ALTER DISKGROUP data OFFLINE DISKS IN FAILGROUP 'fg_0000';

ALTER DISKGROUP data ONLINE DISKS IN FAILGROUP 'fg_0000';

-- Bring online all disks in disk group.

ALTER DISKGROUP data ONLINE ALL;

Disk groups that can't be mounted by ASM can now be dropped using the FORCE keyword of

the DROP DISKGROUP command.

DROP DISKGROUP data FORCE;

How to check how much disk space is allocated/ in-use by an

ASM instance?

Login to your +ASM instance (SYS AS SYSDBA) and execute the following query:

SQL> COL % FORMAT 99.0

SQL> SELECT name, free_mb, total_mb, free_mb/total_mb*100 "%" FROM v$asm_diskgroup;

NAME FREE_MB TOTAL_MB %

------------------------------ ---------- ---------- -----

DATA 917104 1482145 61.9

RECOVER 17387 17437 99.7

From Oracle 10g Release 2, one can also use the asmcmd command line utility:

ASMCMD> du

Used_MB Mirror_used_MB

1523 1523

ASMCMD> lsdg

State Type Rebal Unbal Sector Block AU Total_MB Free_MB

Req_mir_free_MB Usable_file_MB Offline_disks Name

MOUNTED EXTERN N N 512 4096 1048576 11264 9885

0 9885 0 DISKGROUP1/

MOUNTED EXTERN N N 512 4096 1048576 10240 9906

0 9906 0 FLASH/

http://www.orafaq.com/wiki/Asmcmd

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Starting ASMCMD

To start ASMCMD, set your ORACLE_SID to +ASM and then type ASMCMD from the command

line as seen here:

C:\>Set ORACLE_SID=+ASM

C:\>ASMCMD

Or from UNIX:

/opt/oracle>export ORACLE_SID=+ASM

/opt/oracle>ASMCMD

Note: You will need to make sure that perl.exe is in the path before you run ASMCMD. If you have

installed more than one ORACLE_HOME, it may take some setup to get the pathing set correctly.

Make sure the following is set to the correct ORACLE_HOME:

ORACLE_HOME

PATH

PERL5LIB

PERLBIN

When ASMCMD starts, you will see the ASMCMD prompt as seen here:

ASMCMD>

You can start ASMCMD with the –p option and it will display the directory level that you are at as seen

in this example:

C:\oracle\product\10.2.0\DB01\BIN>ASMCMD -p

ASMCMD [+] >

ASMCMD Commands

ASMCMD has a basic set of 16 commands. You can see these commands from the ASMCMD prompt

if you type in help as seen in this output:

ASMCMD> help

ASMCMD [-p] [command]

The environment variables ORACLE_HOME and ORACLE_SID determine the

instance to which the program connects, and ASMCMD establishes a

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bequeath connection to it, in the same manner as a SQLPLUS / AS

SYSDBA. The user must be a member of the SYSDBA group.

Specifying the -p option allows the current directory to be displayed

in the command prompt, like so:

ASMCMD [+DATAFILE/ORCL/CONTROLFILE] >

[command] specifies one of the following commands, along with its

parameters.

Type "help [command]" to get help on a specific ASMCMD command.

commands:

--------

cd

du

find

help

ls

lsct

lsdg

lsdsk

md_backup

md_restore

mkalias

mkdir

pwd

remap

rm

rmalias

cd – Change directory

The cd command will move you in and out of ASM directory structures. This command works just like

it's UNIX equivelent, and the special designators for previous directory ".." are available for use and

use "+" to indicate the root (instead of a forward or backwards slash ( / or \)). Here are some examples:

ASMCMD [+cooked_dgroup1] > cd ..

ASMCMD [+] > cd cooked_dgroup1

ASMCMD [+cooked_dgroup1] > cd +cooked_dgroup2

ASMCMD [+cooked_dgroup2] > cd rob10gr2

du – Disk Used

The du command indicates how much disk has been used on the disk group. Here is an example:

ASMCMD [+cooked_dgroup1/rob10gr2] > du

Used_MB Mirror_used_MB

44 88

find – Find a directory or file

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The find command can help you find a directory or file within the ASM system as seen here:

ASMCMD [+cooked_dgroup1] > find + rob10gr2

+COOKED_DGROUP1/ROB10GR2/

+COOKED_DGROUP2/ROB10GR2/

help

The help command provides you with help for all the ASMCMD commands. You can enter help,

followed by the command name, for more detailed information on the command you are interested in.

ls

The ls command is the list file command. This will list the directories and/or files contained within the

ASM disk structure. Here are some examples of using the ls command:

ASMCMD [+cooked_dgroup1/rob10gr2/datafile] > ls -l

Type Redund Striped Time Sys Name

DATAFILE MIRROR COARSE JAN 29 20:00:00 Y ALIAS_TBS.260.613168611

DATAFILE MIRROR COARSE JAN 29 20:00:00 Y PART_ASM_TBS.256.613066047

DATAFILE MIRROR COARSE JAN 29 20:00:00 Y PART_ASM_TBS.257.613083267

The ls command has new functionality in Oracle 11g adding two new parameters, -c and -g. When used,

the -c parameter will use the V$ASM_DISKGROUP view for the source of its output. Additionally the

-g parameter is used, then GV$ASM_DISKGROUP will be used as the source of the output of the

command. Thus, the ls command becomes "RAC" aware for a clustered ASM instance.

lsct

The lsct command lists all clients that are using ASM. You can specify a disk group to restrict the

output or you can just allow the command to display all the clients. The output of the command

displays the databases connected to the ASM instance, the version of the database connected. Also

included is the compatible version of the database (set via the COMPATIBLE parameter setting) and

the instance name of the instance connected to the ASM instance. Here is an example of the output

from the lsct command:

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > lsct

DB_Name Status Software_Version Compatible_version Instance_Name

rob10gr2 CONNECTED 10.2.0.1.0 10.2.0.1.0 rob10gr2

In Oracle 11g, the lsct command includes the -g parameter, which will cause it to select from the

GV$ASM_CLIENT view rather than the V$ASM_CLIENT view.

lsdg

The lsdg command provides information on the disk groups that have been created in an ASM instance.

This command returns a great deal of information about the disk group. Of particular interest is the

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free_MB column, which indicates how much space is available on the disk group. Here is an example

of the output of the lsdg command:

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > lsdg

State Type Rebal Unbal Sector Block AU Total_MB Free_MB

Req_mir_free_MB Usable_file_MB Offline_disks Name

MOUNTED NORMAL N N 512 4096 1048576 198 22

0 11 0 COOKED_DGROUP1/

MOUNTED NORMAL N N 512 4096 1048576 198 58

0 29 0 COOKED_DGROUP2/

The lsdg command has new functionality in Oracle 11g adding two new parameters, -c and -g. The -c

and -g parameters provide a view into the configuration of a clustered ASM instance. The -c parameter

uses the V$ASM_DISKGROUP view for the source of its output. If the -g parameter is used, then

GV$ASM_DISKGROUP will be used as the source of the output of the command.

lsdsk (Oracle 11g)

The lsdsk command lists the disks that are visible to ASM. Here is an example:

[oracle@localhost ~]$ asmcmd lsdsk

Path

/oracle/asmdata/asm_dgroup1_01.asm

/oracle/asmdata/asm_dgroup1_02.asm

md_restore and md_backup (Oracle 11g)

Commands that allow you to back up and restore the metadata associated with your ASM disk groups.

See below for more information.

mkalias

Use the mkalias command to create ASM aliases for a given ASM file name. This command is

equivalent to the alter diskgroup add alias command from the SQL prompt when connected to an ASM

instance. Here is an example of using the mkalias to create an alias for an ASM file:

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > mkalias

+cooked_dgroup1/rob10gr2/controlfile/Current.258.613087119

+cooked_dgroup1/control01.ctl

One thing to note is that the alias must reside in the same disk group as the ASM file. So the following

command would not be legal:

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > mkalias

+cooked_dgroup1/rob10gr2/controlfile/Current.258.613087119

+cooked_dgroup2/control01.ctl

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mkdir

Mkdir allows you to create ASM directories. You can not create a directory in the root directory (+),

and you can create multiple directories at one time by simply listing them one at a time on the mkdir

command line separated by spaces. This command is roughly equivalent to the alter diskgroup add

directory command. Here are a couple of examples of using the mkdir command:

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > mkdir old

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > mkdir older oldest

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > ls

Current.258.613087119

Current.259.613088323

old/

older/

oldest/

pwd

Use the pwd command to determine where in the ASM directory tree you are. Here is an example:

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > pwd

+cooked_dgroup1/rob10gr2/controlfile

remap (Oracle 11g)

If you find that you have physical blocks corrupted on your ASM disks the new remap command can

be used to repair those blocks. Pass the command the required parameters including the disk group

name, the disk name, and a range of blocks to start the remapping/repaid process. This command does

not repair the data in the blocks, but rather just reconstructs the blocks in an attempt to make them

usable again. As a result, media recovery will still be required after remapping of the block has been

completed. In the following example we are remapping blocks 1000 to 3000 on disk disk_00A assigned

to disk group dgroupA:

[oracle@boots ~]$ asmcmd remap dgroupA disk_00A 1000-3000

rm

The rm command is used to remove ASM directories or files. The rm command will only remove a

directory if that directory is empty. This is equivalent to the alter diskgroup drop directory command.

Here is an example of removing a directory with the rm command:


Current.258.613087119

Current.259.613088323

old/

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older/

oldest/

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > rm old


Current.258.613087119

Current.259.613088323

older/

oldest/

The rm command is also used to remove ASM files and associated aliases. This is equivalent to the

alter diskgroup drop file command. Here is an example of the use of the rm command to remove an

ASM control file:


Current.258.613087119

Current.259.613088323

older/

oldest/

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > rm Current.258.613087119


Current.259.613088323

older/

oldest/

You can use the "*" wildcard character with the rm command too. If you use the wildcard character,

Oracle will warn you to make sure that you truly want to remove the file. Here is an example:


Current.259.613088323

older/

oldest/

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > rm current*

You may delete multiple files and/or directories.

Are you sure? (y/n) y


older/

oldest/

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] >

The rm command also comes with an –r parameter that allows you to recurse child directories. Use the

–r parameter and some file, directory or alias specification. As with the use of the wildcard character,

ASMCMD will query you to make sure you really want to complete the operation as seen in this

example:


older/

oldest/

ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] > rm -r *

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You may delete multiple files and/or directories.

Are you sure? (y/n) y


ASMCMD [+cooked_dgroup1/rob10gr2/controlfile] >

rmalias

The rmalias command is used to remove ASM aliases as seen in this example:

ASMCMD [+cooked_dgroup1/rob10gr2/datafile] > ls

ALIAS_TBS.260.613168611

PART_ASM_TBS.256.613066047

PART_ASM_TBS.257.613083267

ASMCMD [+cooked_dgroup1/rob10gr2/datafile] > mkalias

+cooked_dgroup1/rob10gr2/datafile/part_asm_tbs.256.613066047 +cooked_dgroup1/ro

b10gr2/datafile/alias_tbs_01.dbf

ASMCMD [+cooked_dgroup1/rob10gr2/datafile] > ls +cooked_dgroup1/rob10gr2/datafile

ALIAS_TBS.260.613168611

PART_ASM_TBS.256.613066047

PART_ASM_TBS.257.613083267

alias_tbs_01.dbf

ASMCMD [+cooked_dgroup1/rob10gr2/datafile] > rmalias

+cooked_dgroup1/rob10gr2/datafile/alias_tbs_01.dbf

ASM Diskgroup Metadata Backup and Recover

As of Oracle 11g, asmcmd provides commands that allow you to back up and restore the metadata

associated with your ASM disk groups. You can use the md_backup command to create a backup of all

the ASM metadata, or a subset of ASM metadata, depending on the parameters that you use. Here is an

example of using the md_backup command to back up the entire ASM metadata repository:

[oracle@localhost ~]$ asmcmd

ASMCMD> md_backup

This command will create the metadata backup file in the current working directory by default. On a

Linux system this file was called ambr_backup_intermediate_file. The backup file is pretty much text-

based, so you can read through it. More advanced use of the md_backup command allows you to

control where the backup file will be created, specify the disk groups that you want to back up, and to

override various options. The md_backup command will not overwrite a previous backup file. So you

will need to move the file somewhere after the backup so the next backup will be successful.

You can restore the ASM metadata with the md_restore command. You can restore from the backup

without any changes, or the md_backup command gives you numerous options to override settings too.

In this example we are performing a metadata restore with the md_restore command:

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[oracle@localhost ~]$ asmcmd

ASMCMD> md_restore –b ambr_backup_intermediate_file

Both commands can be run as a parameter from the command line as in this example:

[oracle@localhost ~]$ asmcmd md_backup

So, why would you use md_restore and md_backup? As with Oracle databases there is a possibility that

the ASM metadata stored in the ASM disk groups could become corrupt (perhaps because of some in-

memory OS corruption) or perhaps someone accidently used the dd command and overwrote the

contents of the disk header. While this is probably a rare problem, it is in cases like these that your

ASM metadata backups could come in handy. If you are using ASM, a metadata backup should become

one of your new daily backup operations.

The md_restore command can also reinstate dropped disks, in some cases. Another use of that is

developing an automatic change control process whenever you add, change, or drop disks.

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