ibm system storage svc easy tier in 7 3

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IBM System Storage SAN VolumeController – IBM Easy Tier in 7.3.0 release

Kushal S. Patel, Shrikant V. Karve

IBM Systems and Technology Group ISV Enablement

July 2014

© Copyright IBM Corporation, 2014

https://twitter.com/IBMSystemsISVs


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IBM System Storage SAN Volume Controller – IBM Easy Tier in 7.3.0 release

Table of contents

Abst rac t........................................................................................................................................1

Gett ing started.............................................................................................................................1

Introduction to Easy Tier.......................................................................................................................... 1

User transparency.................................................................................................................................... 1

Migration of extents.................................................................................................................................. 2

What is new in 7.3.0 release.......................................................................................................3

Limiting function.......................................................................................................................................3

Balancing function.................................................................................................................................... 3

Support for three tiers ..............................................................................................................................4

Easy Tier licensing changes ....................................................................................................................4

Easy Tier limitation................................................................................................................................... 5

Customer scenarios....................................................................................................................5

Upgrade to 7.3.0 version ......................................................................................................................... 5

Performance benefits............................................................................................................................. 14

Summary ....................................................................................................................................15

Resources ..................................................................................................................................16

About the authors .....................................................................................................................16

Trademarks and special notices..............................................................................................17


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Abstract

This white paper provides a brief introduction to the IBM System Storage SAN Volume Controller(SVC) cluster with the IBM Easy Tier feature in the 7.3.0 release. The paper gives informationregarding the Easy Tier configuration, management, and upgrade changes in detail.

This paper also provides guidance about configuring the Easy Tier feature in the SVC cluster. Italso describes the Easy Tier licensing changes in the 7.3.0 release compared to the 7.2.0release, along with the upgrade considerations.

Getting started

This section gives a brief idea about the basics of the IBM® Easy Tier® feature along with the

implementation details.

Introduction to Easy Tier

IBM Easy Tier feature is supported with IBM System Storage® SAN Volume Controller (SVC), IBMStorwize® V7000, IBM Storwize V7000 Unified, IBM Storwize V5000, IBM Storwize V3700, and IBM

System Storage DS8000®. This paper describes the functionality in SVC and Storwize products that are

specific to release 7.3.0

IBM Easy Tier is designed to automate data placement throughout the disk pool to improve the efficiency

and performance of the storage system. Easy Tier aims to relocate data (at the extent level) across up to

three-drive tiers automatically and without disruption to application I/O. These operations are transparent

to users and completely handled by the SVC code. This helps users to have the most frequently used dat

or hot data accessible very fast and with lower latency, whereas the archaic data will be stored in a

relatively lower medium of storage. Easy Tier detects when any data extent is heavily in use and moves to

a higher tier of storage. As a result, data is available very fast, without having to shed huge costs.

The key benefit of Easy Tier in 7.3.0 to older versions is that it allows tiering between three tiers. This

increases the performance of the system. It supports data movement across three tiers, and therefore, the

data can be classified in to following three categories based on usage,

Heavily used data (also called hot data)

Moderately used data (also called warm data)

Cold data

Easy Tier stores hot data in the fastest type of disk, that is, on solid-state drives (SSDs) and warm data

and cold data are stored in enterprise disks and nearline SAS disks respectively. Easy Tier algorithm

works in such a way that it always puts heavily used data in the upper storage tier.

User transparency

The Easy Tier feature is completely transparent to the users and manages all data movement without any

explicit user intervention. Data across tier is being migrated when a certain condition is arrived. This

condition checking is automated in this feature. Users can see the extent of movement by cluster CLI

commands such as l svdi skext ent . Some of the transparency details include:



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Moving of inactive data automatically on cheaper storage instead of high-cost SSDs can

save data retrieval time. This also saves the costumers money to buy additional SSDs.

When active hot data is moved from an enterprise disk to an SSD, the user can notice a

significant decrease in latency.

Previously, when only two tiers were supported, there was either fast accessibility or slow

accessibility. But with the introduction of the third tier and dividing the generic_hdd tier intenterprise and nearline, it is possible to achieve better performance even when the tier is

not SSD disks in the system.

Easy Tier supports the load or performance rebalancing feature. Hence from a user's

perspective, latency has been minimized to a substantial level.

For inactive cold data, which is not used often and are mainly for archival purposes, there

is no need to store such data in costly, high-performance SSDs. Instead, it moved to a

cheaper medium: such as nearline, and whenever the data gets hot, it is automatically

moved to a better layer.

Migration of extents

With the extension of support for three tiers, migration attempts to preserve the tier of an extent after user

initiated migration, that is, if an extent is created from a managed disk (MDisk) of enterprise type, then

after migration, it attempts to preserve the tier of the extent, that is, it will seek to conserve it as an

enterprise tier. If an extent of the correct type is not available in the target pool, then it searches for a free

extent from the other tiers in the order: enterprise, nearline, SSD. This is the same order in which creation

and expansion will select extents from MDisks. However, it is possible to override the tier explicitly by

specifying the appropriate MDisks using the -mdi sk option.

During user-initiated migration, Easy Tier management (including balancing function) will be disabled.

Easy Tier measurement continues during migrations if Easy Tier was enabled before the migration started

and will be enabled after the migration completes.

In Easy Tier function of 7.3.0 release, there are basically two types of migration based on tier levels:

Intra-tier migration: The extent migration between the same tier disks is nothing but intra-tier migration.

This type of load balancing is also known as “balancing”. If a system has some highly utilized disks and

some low-utilized disks, then some hot extents from the highly utilized disks are moved to the under-

loaded disks. Here, both the disks are of the same tier.

Inter-tier migration: The extent migration across the tier is also known as inter-tier migration. In this type

of migration, the extent of one tier moves to the other tier disk. This migration can happen if the destinatio

MDisk is the upper tier MDisk and has no performance downgrade after the migration and another MDisk

of lower tier has hot data. This migration can also be called as the extent promote operation. If the upper

tier MDisk has cold data, then this cold data is migrated to the lower tier disk, provided, the destination hasthe capacity to accommodate the extent completely. This cold data migration to lower tier disk is also

known as the cold demote operation. Another scenario can be if the extents on the MDisks are extremely

hot and hitting the performance limit of the MDisk; then the extents are demoted to a lower tier in order to

protect the higher tier performance. This is known as the warm demote operation.



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What is new in 7.3.0 release

There are mainly four new functions introduced in Easy Tier release 7.3.0

Limiting function – This is a new function that handles performance monitoring and

denies extent to migrate if the destination disk is already overloaded or gets overloaded

after extent migration.

Balancing – This function deals with extent migration within the same tier MDisks. This

function is out of Easy Tier licensing.

Support for three tiers – Older Easy Tier supports two technology types, that is, SSD

and hard disk drive (HDD) which are considered as Tier0 and Tier1 respectively. Easy

Tier of 7.3.0 release cares about SSD, enterprise, and nearline. The generic_hdd tier is

split into “enterprise” and “nearline” tier. Therefore the "tier" can have the values "ssd,

enterprise, nearline".

Licensing changes – Significant changes have happened in Easy Tier licensing in the

7.3.0 release. These changes are explained briefly in the following subsections.

Limiting function

Although SSDs have grown in size, they have not grown the same in performance. SSDs can have nasty

characteristics when overloaded; the performance might degrade significantly and abruptly when the SSD

reaches its load capacity. Easy Tier code implementation in versions before release 7.3.0 has nothing to

prevent it from putting too many extents on SSD. Due to this SSD’s performance could actually become

worse. In Easy Tier 7.3.0 release, the limiting function is introduced. This limiting function takes care of the

SSD’s performance and limits the extent migration to SSD when it reaches to performance limit. This

function helps to control extent movement in case of nasty behavior of SSD disks.

Also, in case of external MDisks, Easy Tier collects statistics about the utilization of MDisk. It calculates

the controller performance value and displays through l smdi s k CLI (detailed view only). These values

are sampled into low, medium, high, very_high and blank for array MDisks. The user can change the

controller performance value using the chmdi sk command. The valid values can be default, low, med,

high, and very high. Choosing "default" causes the value to revert to the system determined value. The

"very_high" parameter to this command will only be valid if the tier is "ssd". If the controller performance is

"very_high" and the user changes the tier from "ssd" to "enterprise" or "nearline", the controller

performance value will automatically be changed to "high" (while converse is not true). This functionality is

not supported by cluster GUI.

Balancing function

Balancing is a feature that deals with extent migration within the same storage tier. The extent migrationbetween the same tier MDisks are nothing but intra-tier migration. If a disk is highly utilized (and the other

disks of the same tier than that first are low utilized) then some hot extents are moved to the low-utilized

disk if the low-utilized disk does not reach the performance limit after the migration. Here, both the disks

are of same tier. This feature of balancing is available in all types of tiers and is out of the purview of Easy

Tier licensing. The balancing function improves performance as hotter extents are distributed among



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multiple disks of the same tier. This function plays an important role in overloading scenarios, where exten

migration improves performance by great extent.

Versions before release 7.3.0 require a balancing script to balance the extents across MDisks. By

rebalancing the extents from existing volumes onto new MDisks, existing volumes will get a performance

boost. This balancing script is not required from 7.3.0 release as the balancing function is invoked

immediately after the addition of an MDisk in an MDisk group..

IBM System Storage SVC supports balance capability for single-tier pools. The auto balancing function w

be “on” by default in SVC/Storwize. As most customers prefer to keep management and customer

decision making to a minimum, the best option is to just have that as the default.

Support for three tiers

Versions before Easy Tier release 7.3.0 supports two technology types: SSD and HDD which are

considered as Tier0 and Tier1 respectively. While assigning a value to “tier”, user can pick from a

technology type (generic_ssd, generic_hdd). In Easy Tier until release 7.2.0, this value of “tier” is used for

internal computation. This limitation in earlier versions has been overcome in Easy Tier 7.3.0 release.

In the 7.3.0 release of SVC, Easy Tier cares about SSD, enterprise, and nearline, and therefore, the "tier"

can have the values "ssd, enterprise, nearline". "generic_hdd" in Easy Tier is changed to "enterprise" with

the addition of "nearline". Lowest technology types (such as SSD, enterprise, or nearline) are used if an

MDisk is made from mixed disks rather than what user assigns or overrides.

Easy Tier has multitier support with two independent modes of action: Promotion and demotion (either ca

cause a swap.) Promotion moves an extent up by 1 tier while demotion moves an extent down by one tier

Easy Tier code does not cope up with moving an extent from tier 2 to tier 0 (or from tier 0 to tier 2) in one

go. But, if you have a pool of technology types (such as SSD and nearline) then SSD arrays are mapped

to tier 0 and nearline arrays are mapped to tier 1. Due to this, a two-tier promotion/demotion is avoided.

Easy Tier licensing changes

Easy Tier is a feature that requires a distinct license. The licensing is different for each product type. The

following license restrictions are applicable for various Storwize products.

SVC and Storwize V7000 do not require a license for Easy Tier

Storwize V3500 does not allow Easy Tier

Storwize V3700 requires a license and it is strictly enforced. Setting Easy Tier to “on” has

no impact if Easy Tier is not licensed and when the user acquires a license, Easy Tier

becomes active.

With Storwize V5000, the user is supposed to purchase a license for Easy Tier, but it is

not enforced. Instead, warning messages are produced if the user enables Easy Tier

without a license. Therefore, Easy Tier status will not automatically change to “on” when

upgrading to Storwize V5000. If a user acquires an Easy Tier license for Storwize V5000,

then Easy Tier status becomes active automatically without any additional user action.

This licensing change affects the easy_tier "auto" functionality. The easy_tier auto functionality translates

to on if Easy Tier is licensed or no license is required and is off if Easy Tier is not licensed and a license i

required. Changing Easy Tier from "auto" to "on" will enable Easy Tier when a license is required but the



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license is not strictly enforced. It will have no effect if a license is required and the license is strictly

enforced. Also, changing Easy Tier to "measure" will not have any effect when a license is required and

the license is strictly enforced. Thus the "easy_tier" attribute can then take on the values “auto”, “on”, “off”

and “measure”.

Similarly, the "easy_tier_status" attribute undergoes changes with licensing. The status, "active" will now

mean that Easy Tier is managing the multitier pools while it is “balanced” for a single-tier pool. A new valu

"measured" indicates that Easy Tier statistics are being collected for all vdisks but no management is

taking place. The status, "inactive" means that Easy Tier is neither collecting statistics nor managing the

tiers.

Easy Tier limitation

If the Storwize V3700 setup with a 4 GB node memory reaches above 700k extents, then Easy tier

functionality gets automatically disabled and error message 020007 (storage optimization services

disabled) is flagged. This error disappears automatically after the addition of canister RAM or molding

setup to less than 700k extents.

Customer scenarios

This section includes customer scenarios namely upgrade to 7.3.0 version and performance benefits.

Upgrade section mainly includes CLI changes in upgrade to 7.3.0. The other subsections talks about the

performance benefits of the Easy Tier functionality of the 7.3.0 version. This includes performance benefit

of Easy Tier and snaps of performance statistics graphs.

Upgrade to 7.3.0 version

Upgrade is actually fairly simple. While upgrading from older versions to the 7.3.0 version, some changes

can be observed by custumers. Compatibility has two aspects namely, task commands and list

commands. With respect to task commands, 7.3.0 code continues to accept prior (now superseded)

values and map them to an appropriate value. If the user enters "generic_hdd" on the command line in a

situation where it is possible to specify a "tier" value, then that will be accepted and mapped to

"enterprise". Similarly "generic_ssd" will map to the “ssd” tier.

With respect to list commands, if the setting of pools (both single tier and multiple tiers) is

“easy_tier = auto”, it remains unchanged, and the status of the pool becomes “easy_tier = active” (if

permitted by licensing), and the volumes' setting remains unchanged, but the status gets updated

accordingly. For the volumes in the "auto" single-tier pool, the “easy_tier_status” will become "balanced",

and others remain same. A multitier MDisk group with "easy_tier" of "on" will be unchanged. A pool

(consisting of multiple tier and single tier) with "easy_tier" of "off" will be unchanged. For a single tierMDisk group with "easy_tier" of "on", the status will be inactive. If Easy Tier is not licensed, a license is

required and it is strictly enforced. An MDisk group whose "easy_tier" attribute is "off" will be unchanged.



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Figure 1: lsmdisk command output in 7.2.0 version

After upgrading to 7.3.0 build, MDisks’ tier values are changed. “generic_ssd” becomes “ssd”,

“generic_hdd” layer is split into “enterprise” and “nearline” tiers.

Figure 2: lsmdisk command output after upgrade to 7.3

7.2.0 Version shows below output (Figure 3) after execution of lsmdiskgrp command. Here mdiskgrp 0 is

made from all three types of tiers. This command shows easy_tier status along with tier_mdisk_count for

each tier in mdiskgrp.



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Figure 3: lsmdiskgrp command – detailed view of mdiskgrp 0 in 7.2.0 version

After upgrading to 7.3.0 version, if license is provided to the system or if it is not strictly enforced, then

hybrid tier pool’s MDisk group parameters that are “easy_tier” and “easy_tier_status” remains unaffected

If license is not provided in case it is strictly enforced, then the “easy_tier” parameter will as before

upgrade while “easy_tier_status” will be “inactive”. In this case, the “generic_hdd” tier is split into

“enterprise” and “nearline” tiers and all three tier values are shown as part of the l s mdi s kgr p command.



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Figure 4: lsmdiskgrp command output for mdiskgrp 0 after upgrade to 7.3.0 version

In the case of pool 1 which is made up from two MDisks, one is an “enterprise” MDisk and another is a

“nearline” MDisk. As versions before Easy Tier 7.3.0 has only two tiers, it is showing both as “generic_hdd

and hence “tier_mdisk_count” is two. As Easy Tier 1 handles enterprise and nearline disks as

generic_hdd, the tier_mdisk_count of this pool is two.



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Figure 5: lsmdiskgrp command – a detailed view of mdiskgrp 1 in 7.2.0 version

After upgrading to 7.3.0 version, as three tiers are supported, all the entries of mdiskgrp are recalculated

and filled accordingly. Due to this, one pool1 MDisk is recognized as “nearline” and tier_mdisk_count is

recalculated as shown in Figure 6.



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Figure 6: lsmdiskgrp command output for mdiskgrp 1 after upgrading to 7.3 version



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Figure 7: lsmdiskgrp command output for single tier mdiskgrp 2 before upgrading to 7.3.0 version



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Figure 8: lsmdiskgrp command output for single tier mdiskgrp 2 after upgrading to 7.3.0 version



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Figure 9: Cluster GUI showing MDisks and tiers in a version before 7.3.0

Figure 10: Cluster GUI showing MDisks and tiers in 7.3.0 version



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Performance benefits

After the Easy Tier feature is activated in the system, customers can see improved performance statistics

This performance benefit is in terms of improved I/O rate and reduction in latency period. As Easy Tier

move hot extents to upper tier which has high performance capability, the overall performance of the

system increases and the read/write operation becomes faster.

Considering a scenario in which a volume is created from a pool of an SSD and a nearline MDisk. In this

example, volume extents are on the nearline MDisk and hence all read/write operations are on extents of

nearline disks. As Easy Tier is active in the system, it monitors all the I/O operations happening in the poo

and migrates hotter extents to the upper tier. In this case, the upper tier that is available in the pool is SSD

The following screen captures show details of performance improvement due to extent migration by Easy

Tier.

Figure 11: Improvement in read I/O by Easy Tier extent migration



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Figure 12: Improvement in write I/O by Easy Tier extent migration

Summary

This white paper provides a brief introduction to the IBM System Storage SVC cluster with the IBM Easy

Tier feature in the 7.3.0 release along with upgrade considerations. In the 7.3.0 version, three-tier support

is introduced along with the balancing function. The limiting function handles performance monitoring and

denies extent to migrate if the destination disk is already overloaded or gets overloaded after extent

migration. The balancing function deals with extent migration within the same storage tier. Due to the

balancing function, the balancing script is not required from the 7.3.0 release. Significant changes have

happened in Easy Tier licensing in the 7.3.0 release which is also covered in detail. The IBM Easy Tierfeature improves performance by moving hotter extents to upper high-speed tier and cold extents to the

lower tier disk. Moving of inactive data automatically on cheaper storage instead of high-cost SSDs can

save data retrieval time. This also saves the costumer’s money to buy additional SSDs.



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Resources

The following websites provide useful references to supplement the information contained in this paper:

IBM Systems on PartnerWorld®ibm.com/partnerworld/systems

IBM Power Development Platform

ibm.com/partnerworld/pdp

IBM Power Systems Information Center

http://publib.boulder.ibm.com/infocenter/powersys/v3r1m5/index.jsp

IBM Redbooks®

ibm.com/redbooks

About the authors

Kushal S. Patel is an associate software engineer in IBM Systems and Technology Group SVC and

Storwize family. As part of Easy Tier team, he was the member of functional test execution. You can reac

Kushal at [email protected].

Shrikant V. Karve is a storage architect in IBM Systems and Technology Group SVC and Storwize family

As part of the Easy Tier team, he was the functional test lead. You can reach Shrikant at

[email protected]


https://twitter.com/IBMSystemsISVs


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Trademarks and special notices

© Copyright IBM Corporation 2014.

References in this document to IBM products or services do not imply that IBM intends to make them

available in every country.

IBM, the IBM logo, and ibm.com are trademarks or registered trademarks of International Business

Machines Corporation in the United States, other countries, or both. If these and other IBM trademarked

terms are marked on their first occurrence in this information with a trademark symbol (® or ™), these

symbols indicate U.S. registered or common law trademarks owned by IBM at the time this information

was published. Such trademarks may also be registered or common law trademarks in other countries. A

current list of IBM trademarks is available on the Web at "Copyright and trademark information" at

www.ibm.com/legal/copytrade.shtml.

Other company, product, or service names may be trademarks or service marks of others.

Information is provided "AS IS" without warranty of any kind.

All customer examples described are presented as illustrations of how those customers have used IBM

products and the results they may have achieved. Actual environmental costs and performance

characteristics may vary by customer.

Information concerning non-IBM products was obtained from a supplier of these products, published

announcement material, or other publicly available sources and does not constitute an endorsement of

such products by IBM. Sources for non-IBM list prices and performance numbers are taken from publicly

available information, including vendor announcements and vendor worldwide homepages. IBM has not

tested these products and cannot confirm the accuracy of performance, capability, or any other claims

related to non-IBM products. Questions on the capability of non-IBM products should be addressed to the

supplier of those products.

All statements regarding IBM future direction and intent are subject to change or withdrawal without notice

and represent goals and objectives only. Contact your local IBM office or IBM authorized reseller for the

full text of the specific Statement of Direction.

Some information addresses anticipated future capabilities. Such information is not intended as a definitiv

statement of a commitment to specific levels of performance, function or delivery schedules with respect t

any future products. Such commitments are only made in IBM product announcements. The information is

presented here to communicate IBM's current investment and development activities as a good faith effor

to help with our customers' future planning.

Performance is based on measurements and projections using standard IBM benchmarks in a controlled

environment. The actual throughput or performance that any user will experience will vary depending upo

considerations such as the amount of multiprogramming in the user's job stream, the I/O configuration, the

storage configuration, and the workload processed. Therefore, no assurance can be given that an

individual user will achieve throughput or performance improvements equivalent to the ratios stated here.

Photographs shown are of engineering prototypes. Changes may be incorporated in production models.



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Any references in this information to non-IBM websites are provided for convenience only and do not in

any manner serve as an endorsement of those websites. The materials at those websites are not part of

the materials for this IBM product and use of those websites is at your own risk.

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