24 Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.1
Child storage pools
Instead of being created directly from MDisks, child pools are created from existing capacity
that is allocated to a parent pool. As with parent pools, volumes can be created that
specifically use the capacity that is allocated to the child pool. Parent pools grow
automatically as more MDisks are allocated to them. However, child pools provide a fixed
capacity pool of storage. You can use a child pool to manage a quota of storage for a
particular purpose.
Child pools can be created by using the management GUI, CLI, or IBM Spectrum Control
when you create VMware vSphere virtual volumes. For more information about child pools,
see Chapter 4, “Storage pools” on page 143.
Single-tiered storage pool
MDisks that are used in a single-tiered storage pool must have the following characteristics to
prevent performance problems and other problems:
They must have the same hardware characteristics, for example, the same RAID type,
RAID array size, disk type, and disk revolutions per minute (RPMs).
The disk subsystems that provide the MDisks must have similar characteristics, for
example, maximum input/output operations per second (IOPS), response time, cache, and
throughput.
You need to use MDisks of the same size and ensure that the MDisks provide the same
number of extents. If this configuration is not feasible, you must 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, for example,
a storage pool that contains a mix of generic_hdd
and generic_ssd MDisks.
A multi-tiered storage pool contains MDisks with different characteristics unlike the
single-tiered storage pool. MDisks with similar characteristics then form the tiers within the
pool. However, each tier needs to have MDisks of the same size and that provide the same
number of extents.
A multi-tiered storage pool is used to enable automatic migration of extents between disk tiers
by using the IBM Storwize V5000 Gen2 IBM Easy Tier function, as described in Chapter 9,
“Advanced features for storage efficiency” on page 437.
This functionality can help improve the performance of host volumes on the IBM Storwize
V5000.
1.6.9 Volumes
A volume is a logical disk that is presented to a host system by the clustered system. In our
virtualized environment, the host system has a volume that is mapped to it by IBM Storwize
V5000 Gen2. IBM Storwize V5000 Gen2 translates this volume into a number of extents,
which are allocated across MDisks. The advantage with storage virtualization is that the host
is decoupled from the underlying storage, so the virtualization appliance can move around the
extents without affecting the host system.
The host system cannot directly access the underlying MDisks in the same manner as it can
access RAID arrays in a traditional storage environment.
The following types of volumes are available:
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