cmsc 691x, summer 1999 honglin su, csee umbc1 chapter 11, backups honglin su csee, umbc...

CMSC 691X, Summer 1999

Honglin Su, CSEE UMBC 1

Chapter 11, Backups

Honglin Su

CSEE, UMBC

hosu@cs.umbc.edu

CMSC 691X, Summer 1999

Honglin Su, CSEE UMBC 2

Agenda

• Introduction• Backup Devices and Media• Incremental Backup• Backup Rules• Restoring from Dumps• Dumping and Restoring from Upgrades• Other Archiving Programs• Summary

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Introduction

• Information stored on computers is worth more than the computers themselves– Consider your accounts stored in Banks

• Hundreds of ways to lose data.– Accidental file removal, External/Internal failures

• Backup - The most efficient and convenient way to protect your data

• Backup must be done carefully and on a strict schedule

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Backup Devices and MediaMedium Capacity Cost Cost/MB Type Reuse Random

FloppyDisk

2.8 MB $0.5 17.60 c M Yes Yes

QIC 150 MB $20 13.30 c M Yes No

Nine-track

160 MB $10 6.25 c M Yes No

Floptical 200 MB $15 7.50 c M/O Yes Yes

WCD-ROM

600MB $10 1.67 c B/O No Yes

Exabyte(8mm)

5 GB+ $9 <0.18 c M Yes No

DAT(4mm)

5 GB+ $7 <0.14 c M Yes No

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Backup Devices and Media

• Most media use magnetic particles to store their data, these media are subject to damage by electrical and magnetic fields.

• New Trends– Larger capacity devices, such as Tape libraries, using

robot; others, e.g. Jukeboxes and Stackers

– Higher speed: 12 MB/s

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Incremental Backup

• dump: builds a list of files that have been modified since a previous dump, then packs those files into a single large file to archive to an external device.– Backups can span multiple tapes

– Files of any type (even devices) can be backed up and restored

– Permission, ownerships, and modify times can be restored

– Files with holes are handled correctly

– Backups can be performed incrementally

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Incremental Backup

• Limitation of dump: – Every filesystem must be dumped individually

• If you have a disk that is partitioned , you must dump each section of the disk separately

– The other limitation is that only filesystems on the local machine can be dumped

• You can not dump an NFS filesystem, however, rdump can dump a local filesystem to a remote tape drive

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Incremental Backup

Maintenance Commands ufsdump(1M) NAME ufsdump - incremental file system dump SYNOPSIS /usr/sbin/ufsdump [options] [arguments] files_to_dump DESCRIPTION ufsdump backs up all files specified by files_to_dump (nor- mally either a whole file system or files within a file sys- tem changed after a certain date) to magnetic tape, diskette, or disk file. When running ufsdump, the file sys- tem must be inactive; otherwise, the output of ufsdump may be inconsistent and restoring files correctly may be impos- sible. A file system is inactive when it is unmouned or the system is in single user mode. A file system is not con- sidered inactive if one tree of the file system is quiescent while another tree has files or directories being modified.

Solaris LinuxDUMP(8) UNIX System Manager's Manual DUMP(8) NAME dump - filesystem backup SYNOPSIS dump [0123456789BbhfusTdWn [argument ...]] filesystem dump [0123456789BbhfusTdWn [argument ...]] directory DESCRIPTION Dump examines files on a filesystem and determines which files need to be backed up. These files are copied to the given disk, tape or other stor- age medium for safe keeping (see the f option below for doing remote backups). A dump that is larger than the output medium is broken into multiple volumes. On most media the size is determined by writing until an end-of-media indication is returned. On media that cannot reliably return an end-of-media indication (such as some cartridge tape drives) each volume is of a fixed size; the actual size is determined by the tape size and density and/or block count options below. By default, the same output file name is used for each volume after prompting the operator to change media.

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Incremental Backup

• Backup level 0 ~ 9– A level zero backup places the entire filesystem on the

tape

– A level N dump backs up all files that have changed since the last dump level less than N.

– To restore files from several sets of backup tapes to reset a filesystem to its exact state during the last backup.

• dump does not care about the length of filename.

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Incremental Backup

• Dump sequences and schedule– The schedule that is right for you depends on

• The activity of your filesystems

• The capacity of your dump device

• The amount of redundance you want

• The number of tapes you want to buy

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Backup Rules

• Perform all dumps from one machine– using rdump, there is a performance penalty, while the

ease of administration makes it worthwhile.

• Label your tapes: exalabel• Pick a reasonable backup interval

– The more often backups are done, the smaller the amount of data that can be lost in a crash

• Choose filesystems carefully

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Backup Rules

• Make daily dumps fit on one tape• Make filesystems samller than your dump device• Keep tapes off-site• Limit Activity during dumps• Check your tapes

– Verify that the tape contains the expected files

• Prepare for the worst

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Restoring from Dumps

• Restoring individual files– restore x filename

– use rrestore to extract files from rdump.

– If multiple files on a single tape, use mt to position the tape at the correct dump file before running restore

• Interactive restore– If your version of restore supports the i option.

• Restore entire filesystems– restore r

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Dumping and Restoring for Upgrades

• When you perform an OS upgrade, all filesystems must be backed up with a level zero dump.

• Be sure to back up and restore any system-specific files that are in / or /usr, such as /etc/passwd, /usr/local, etc.

• Your should do a complete set of level zero dumps immediately after an upgrade.

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Other Archiving Programs

• tar: Package Files• cpio: ATT-ish Archiving, copy file archives in and

out, similar to tar• dd: Twiddle Bits

– % dd if=/dev/rmt0 of=/dev/rmt1 cbs=16b

• volcopy: Duplicate Filesystems

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Other Archiving Programs

• tarUser Commands tar(1) NAME tar - create tape archives and add or extract files SYNOPSIS tar c [bBefFhiklnopPqvwX [ 0-7 ]] [ block ] [ tarfile ] [ exclude-file ] { -I include-file | -C directory file | file } ... tar r [ bBefFhiklnqvw [ 0-7 ]] [ block ] { -I include-file | -C directory file | file } ... tar t [ BefFhiklnqvX [ 0-7 ]] [ tarfile ] [ exclude-file ] { -I include-file | file } ... tar u [ bBefFhiklnqvw [ 0-7 ]] [ block ] [ tarfile ] file ... tar x [ BefFhiklmnopqvwX [ 0-7 ]] [ tarfile ] [ exclude-file ] [ file ... ]

actaeon.cs.umbc.edu[130] tar cvf tmp.tar tmpa tmp/ 0Ka tmp/yt.hm 12Ka tmp/review1.txt 2Ka tmp/email 2Ka tmp/Map.ppt 31Ka tmp/bob.c 1Kactaeon.cs.umbc.edu[132] tar xvf tmp.tarx tmp, 0 bytes, 0 tape blocksx tmp/yt.hm, 11360 bytes, 23 tape blocksx tmp/review1.txt, 1163 bytes, 3 tape blocksx tmp/email, 1201 bytes, 3 tape blocksx tmp/Map.ppt, 31232 bytes, 61 tape blocksx tmp/bob.c, 61 bytes, 1 tape blocks

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Using multiple files on a single tape

• mt command– rew - rewind the tape to the beginning

– offl - put the tape off-line

– status - show the status of the tape drive

– fsf [count] - fast-forwards the tape

– bsf [count] - backspace count files

actaeon.cs.umbc.edu[137] mtusage: mt [ -f device ] command [ count ]

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Summary

• Related chapters– Chapter 4, The filesystem

– Chapter 7, Devices and drivers

– Chapter 9, Adding a disk

– Chapter 10, Periodic Processes

– Chapter 17, NFS

• For more information– http://www.admin.com/

– http://wwwhost.cc.utexas.edu/cc/services/unix/index.html

• Q & A

• Thank you!