Chapter 9. Advanced features for storage efficiency 447
9.2.12 Easy Tier rules
The following operating rules apply when IBM System Storage Easy Tier is used on the IBM
Storwize V5000 Gen2:
Automatic data placement and extent I/O activity monitors are supported on each copy of
a mirrored volume. Easy Tier works on each copy independently of each other.
Easy Tier works with all striped volumes, including these types of volumes:
– Generic volumes
– Thin-provisioned volumes
– Mirrored volumes
– Thin-mirrored volumes
– Global and Metro Mirror sources and targets
Easy Tier automatic data placement is not supported for image mode or sequential
volumes. I/O monitoring for these volumes is supported, but you cannot migrate extents on
these volumes unless you convert image or sequential volume copies to striped volumes.
The IBM Storwize V5000 Gen2 creates volumes or volume expansions by using extents
from MDisks from the Enterprise and Nearline tier. Extents from MDisks in the Flash tier
are used if Enterprise space and Nearline space are not available.
When a volume is migrated out of a storage pool that is managed with Easy Tier,
Automatic Data Placement Mode is no longer active on that volume. Automatic Data
Placement is also turned off while a volume is migrated, even if it is between pools that
both have Easy Tier Automatic Data Placement enabled. Automatic Data Placement for
the volume is re-enabled when the migration is complete.
Flash drive performance depends on block size. (Small blocks perform better than large
blocks.) Easy Tier measures I/O blocks that are smaller than 64 KB, but it migrates the
entire extent to the appropriate disk tier.
As extents are migrated, the use of smaller extents makes Easy Tier more efficient.
The first migration starts about 1 hour after Automatic Data Placement Mode is enabled. It
takes up to 24 hours to achieve optimal performance.
In the current IBM Storwize V5000 Gen2 Easy Tier implementation, it takes about two
days before hotspots are considered moved from tier to tier, which prevents hotspots from
being moved from a fast tier if the workload changes over a weekend.
If you run an unusual workload over a longer period, Automatic Data Placement can be
turned off and turned on online to avoid data move.
Volume mirroring: Volume mirroring can have different workload characteristics for
each copy of the data because reads are normally directed to the primary copy and
writes occur to both copies. Therefore, the number of extents that Easy Tier migrates
probably differs for each copy.
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