IBM System Storage SAN Volume Controller IBM Easy Tier enhancements in release

Transcription

1 IBM System Storage SAN Volume Controller IBM Easy Tier enhancements in release Kushal S. Patel, Shrikant V. Karve, Sarvesh S. Patel IBM Systems, ISV Enablement July 2015 Copyright IBM Corporation, 2015

2 Table of contents Abstract... 2 Getting started... 2 Introduction to Easy Tier... 2 Migration of extents... 2 What is new in release... 3 Improvement in Easy Tier migration rate... 3 Easy Tier 3 warm demote optimization... 4 Real life use cases... 5 CLI addition in version Summary... 6 Resources... 7 About the authors... 7 Trademarks and special notices... 8

3 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 release. The paper gives information regarding the Easy Tier enhancements in release in detail. Easy Tier enhancements include improvement in Easy Tier migration rate and Easy Tier warm demote optimization. This paper also provides information about command-line interface (CLI) changes along with some customer scenarios of the Easy Tier feature in the SVC cluster. 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 The IBM Easy Tier feature is supported with IBM System Storage SAN Volume Controller (SVC), IBM Storwize 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 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 are completely handled by the SVC code. This helps users to have the most frequently used data or hot data accessible very quickly 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 quickly, without having to shed huge costs. The key benefit of Easy Tier in compared to older versions is that it allows tiering between three tiers along with low workload rebalance improvement, migration rate improvement, and warm demote optimization. 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 flash drives, and warm data and cold data are stored in enterprise disks and nearline serial-attached SCSI (SAS) disks respectively. In terms of Easy Tier, the faster storage is known as upper tier and relatively slower one is lower tier. The Easy Tier algorithm works in such a way that it always puts the heavily used data in the upper storage tier. Migration of extents With the extension of support for three tiers, migration attempts to preserve the tier of an extent if it was the user who initiated migration. That is, if an extent is created from a managed disk (MDisk) of enterprise tier type, then after migration, it attempts to preserve the tier of the extent, that is, it will seek to conserve 2

4 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, solid-state drive (SSD). This is the same order in which VDisk creation and expansion will select extents from MDisks. However, it is possible to override the tier explicitly by specifying the appropriate MDisks using the -mdisk option. If Easy tier was enabled before the user-initiated migration started, Easy Tier management (including balancing function) will be disabled during the migration and re-enabled after the migration completes, but Easy Tier measurement continues during the migration. The extent of 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 destination 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 has the 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. What is new in release There are mainly two new functions introduced in Easy Tier release Improvement in Easy Tier migration rate This is a new function that handles accelerated movement of extents when enabled using CLI. Easy Tier 3 warm demote optimization This function deals with the warm demote optimization operation in the Easy Tier process. Version also enables warm demote operation from Enterprise tier to nearline tier. As a part of optimization of the warm demote operation, the Easy Tier process picks the coldest extent in the tier to demote if warm demote is required to create the space for promotion of the lower tier extent. Improvement in Easy Tier migration rate Versions before Easy Tier release supports a fixed number of extents to be migrated per time. In version, Easy Tier limits extent migrations by the amount of data rather than the number of extents. This limit applies to both balancing function and Easy Tier intra-tier migrations. Also, this limit is cluster wide and not dependent on the I/O group. As the extent size reduced, total data migrated also reduced in versions before release. This led to under utilizing the SSDs and delayed performance benefits. In release 7.5.0, another function is introduced and this accelerates the extent migration. Extent migration limit is now dynamic in nature and is proportional to the extent size. This helps to balance additional migrations along with system performance and you need to take care of the following two are major considerations for this function: 3

5 Number of moved extents is proportional to the extent size. Limitation to the accelerated migration rate to avoid too large migration rate brings bad impact to system performance. The default rate ensures that migrations do not impact system performance. Version before Easy Tier release supports maximum movement of limit of 12 extents per 5 minutes. In this version of 7.5.0, maximum of 12 GiB data per 5 minutes is allowed by Easy Tier to be moved without enabling the acceleration mode. With the acceleration mode enabled, the Easy Tier process moves to a maximum of 48 GiB per 5 minutes. The real migration rate is automatically adjusted based on the host workload but never goes beyond the maximum rate allowed by Easy Tier. User should not normally enable the accelerated mode. Users should temporarily enable the accelerated mode to rapidly use the new capacity, for example: At the time of introduction of additional capacity to an existing storage pool. This can include either adding storage to an existing tier or to a new tier in the pool. Enabling the accelerated mode allows the system to quickly spread the existing volumes into the new capacity. At the time of migrating multiple volumes between pools, and the target pool has more tiers than the source pool. Volume migration between storage pools preserves the tier of the volume's extents. Enabling the accelerated mode allows the system to quickly take advantage of the additional tiers in the target pool. Default value of acceleration mode is off. It is recommended that the accelerated mode should principally be used during periods of lower system activity to avoid the possibility of performance issues caused by overloading the managed disks. Easy Tier 3 warm demote optimization 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. In such cases, warm demote operation is performed. The demote operation is also done to create space for a lower tier extent for promotion. Bandwidth overloading normally means that there are too many large I/O operations on the MDisk. After the tier is bandwidth overloaded, its performance downgrades sharply. So, to protect overloading MDisk's performance, Easy Tier moves the highest bandwidth extent (large sequential I/O operations) to lower tier. Easy Tier warm demote performs the following two major jobs: Protect the performance of upper tier That is, if MDisk is found bandwidth overloading, Warm demote move the highest bandwidth extent of the MDisk to lower tier if the migration does not cause the MDisk of lower tier bandwidth overloading. 4

6 Space reservation Easy Tier migration always need extra free extents on the destination tier. For example, warm demote needs a free extent in the lower tier, Promote needs a free extent in the upper tier, and rebalance which balances workload within a single tier needs free extents in the lower-utilized MDisk. If the tier's free extents are below the required free extents, warm demote happens to free extent by demoting one cold extent to lower tier. In the versions before 7.5.0, warm demote moves the highest bandwidth extent from the SSD tier to the Enterprise tier, which might lead to lower tier bandwidth overloading and downgrading of system performance. This IBM SVC version enables warm demote from the Enterprise tier to nearline tier only for space reservation. If warm demote is required for space reservation, the extent with the lowest peak bandwidth is demoted to the lower tier. It also checks the performance limit for warm demote. Extent demotion is not initiated if it is found to cause lower tier overloading. Real life use cases This section includes customer scenarios, namely CLI addition in version and Easy Tier migration rate improvement demonstration with comparison of release. CLI addition in version In version of SVC, a command parameter is added in the chsystem command from where users can enable or disable the accelerated migration rate of Easy Tier. Easy Tier acceleration enablement is CLI-based and cannot be controlled from GUI. Figure 1: chsystem command to enable the Easy Tier acceleration mode in the version Figure 2: chsystem command to disable Easy Tier acceleration mode in the version 5

7 Figure 3: lssystem command to get Easy Tier acceleration mode in the version Summary This white paper provided a brief introduction to the IBM System Storage SVC cluster with the IBM Easy Tier feature enhancements in the release. In the version, Improvement in Easy Tier Migration Rate is introduced along with Warm demote optimization. The Migration rate improvement handles the accelerated extent movement in balancing and inter-tier migrations. This feature is useful during the addition of storage capacity to an existing storage pool. This addition can either be adding to an existing tier or adding a new tier to the pool. Enabling the accelerated mode allows the system to quickly spread the existing volumes into the new capacity. Easy Tier warm demote optimization enables warm demote from the Enterprise tier to the nearline tier for space reservation. Warm demote for space reservation is done with the movement of the extent with the lowest peak bandwidth to the lower tier. This warm demote optimization also checks the performance limit for warm demote. Demotions are not done if it is found to cause lower tier overloading. 6

8 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 IBM Redbooks ibm.com/redbooks About the authors Kushal S. Patel is an associate software engineer in the IBM Systems and Storwize family. You can reach Kushal at Shrikant V. Karve is a storage architect in the IBM Systems SVC and Storwize family. You can reach Shrikant at shrkarve@in.ibm.com Sarvesh S. Patel is a senior staff software engineer in IBM Systems SVC and Storwize family. You can reach Sarvesh at sarvepat@in.ibm.com. 7

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