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.