Chapter 9. Advanced features for storage efficiency 441
9.2.2 Tiered storage pools
With the IBM Storwize V5000 Gen2, we must differentiate between the following types of
storage pools:
Single-tiered storage pools
Multi-tiered storage pools
Figure 9-2 shows single-tiered storage pools which include one type of disk tier attribute.
Each disk, ideally, has the same size and performance characteristics. Multi-tiered storage
pools are populated with two or more different disk tier attributes, high-performance flash
drives, enterprise SAS drives, and Nearline drives.
A volume migration occurs when the complete volume is migrated from one storage pool to
another storage pool. An Easy Tier data migration moves only extents inside the storage pool
to different performance attributes.
Figure 9-2 Tiered storage pools
By default, Easy Tier is enabled on any pool that contains two or more classes of disk drives.
The Easy Tier function manages the extent migration:
Promote
Moves the candidate hot extent to a higher performance tier.
Warm demote:
– Prevents performance overload of a tier by demoting a warm extent to a lower tier.
– Triggered when bandwidth or I/O per second (IOPS) exceeds a predefined threshold.
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