Implementing the IBM Storwize V5000

Chapter 9. Easy Tier 413

You can enable Easy Tier for storage on a volume basis. It monitors the I/O activity and

latency of the extents on all Easy Tier enabled volumes over a 24-hour period. Based on the

performance log, it creates an extent migration plan and dynamically moves high activity or

hot extents to a higher disk tier within the same storage pool. It also moves extents whose

activity dropped off (or cooled) from higher disk tier MDisks back to a lower tier MDisk.

To enable this migration between MDisks with different tier levels, the target storage pool must

consist of different characteristic MDisks. These pools are named

multitiered storage pools.

IBM Storwize V5000 Easy Tier is optimized to boost the performance of storage pools that

contain HDDs and SSDs.

To identify the potential benefits of Easy Tier in your environment before actually installing

higher MDisk tiers (such as, SSDs), it is possible to enable the Easy Tier monitoring volumes

in single-tiered storage pools. Although the Easy Tier extent migration is not possible within a

single-tiered pool, the Easy Tier statistical measurement function is possible. Enabling Easy

Tier on a single-tiered storage pool starts the monitoring process and logs the activity of the

volume extents. In this case, Easy Tier creates a migration plan file that can then be used to

show a report on the number of extents that is appropriate for migration to higher level MDisk

tiers, such as, SSDs.

The STAT is a no-cost tool that helps you to analyze this data. If you do not have an IBM

Storwize V5000, use Disk Magic to get a better idea about the required number of SSDs that

is appropriate for your workload. If you do not have any workload performance data, a good

starting point can be to add approximately 5% of net capacity of SSDs to your configuration.

However, this ratio is heuristics-based and changes according to different applications or

different disk tier performance in each configuration. For database transactions, a ratio of fast

SAS or Fibre Channel (FC) drives to SSD is about 6:1 to achieve the optimal performance,

but this ratio depends on the environment on which it is implemented.

Easy Tier is available for IBM Storwize V5000 internal volumes and volumes on external

virtualized storage subsystems because the SSDs can be internal or external drives.

However, from the fabric point of view, it is a best practice to use SSDs inside the IBM

Storwize V5000 (even if the lower tiered disk pool is on external storage) because this

configuration reduces the traffic that is traversing the SAN environment.

9.2 Easy Tier for IBM Storwize V5000

This section describes the terms and gives an example implementation of Easy Tier on the

IBM Storwize V5000. After reading this section, you should understand the Easy Tier concept

as it relates to the IBM Storwize V5000.

9.2.1 Disk tiers

It is likely that IBM Storwize V5000 internal disks and external disks have different

performance attributes. As described in Chapter 7, “Storage pools” on page 295, without

Easy Tier, it is a best practice to place drives with the same attributes (the number of

revolutions per minute, size, and type) in the same storage pool, and not to intermix different

drives with different attributes. This configuration is also valid for external MDisks that are

grouped into storage pools. All internal HDDs and external MDisks are initially put into the

generic_hdd tier by default. An internal SSD is identified as a high-performance tier MDisk by

IBM Storwize V5000 and all external SSD MDisks must be changed to the high-performance

tier, as described in Chapter 7, “Storage pools” on page 295.