IBM V7000 Introduction And Implementation Manual page 86

Use the same extent size for all storage pools in a storage system, when they are supporting
volume migration between two storage pools. If the storage pool extent sizes are not the
same, this will not be possible. Use volume mirroring to copy volumes between storage pools,
as described in Chapter 10, "Volume mirroring and migration" on page 447.
For most IBM Flex System V7000 Storage Nodes, a maximum of capacity of 1 PB is
sufficient; and an extent size value of 256 MB should be used.
Default extent size: The GUI of IBM Flex System V7000 Storage Node sets a default
extent size value of 256 MB when you define a new storage pool.
A storage pool can have a threshold warning set that automatically issues a warning alert
when the used capacity of the storage pool exceeds the set limit.
Single-tiered storage pool
MDisks that are used in a single-tiered storage pool need to have the following characteristics
to prevent performance and other problems:
They must have the same hardware characteristics, disk type, disk size, and disk speeds
(revolutions per minute (rpms)).
They must have the same RAID type, RAID array size, and disk spindle count in the RAID
grouping.
The disk subsystems providing the MDisks must have similar characteristics, for example,
maximum input/output operations per second (IOPS), response time, cache, and
throughput.
When possible, make all MDisks of the same size, and ensure that the MDisks provide the
same number of extents per volume. If this configuration is not feasible, you need to check
the distribution of the volumes' extents in that storage pool.
Multi-tiered storage pool
A multi-tiered storage pool has a mix of MDisks with more than one type of disk tier attribute,
for example, a storage pool containing a mix of generic_hdd AND generic_ssd MDisks.
A multi-tiered storage pool contains MDisks with different characteristics as opposed to the
single-tiered storage pool. However, each tier should have MDisks of the same size and
MDisks that provide the same number of extents.
66
IBM Flex System V7000 Storage Node Introduction and Implementation Guide