IBM DS8700, Introduction And Planning Manual

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To extract the summary performance data generated by the Storage Tier Advisor
Tool, you can use either the DS CLI or DS Storage Manager. When you extract
summary data, two files are provided, one for each server in the storage facility
image (SFI server). The download operation initiates a long running task to collect
performance data from both selected storage facility images. This information can
be provided to IBM if performance analysis or problem determination is required.
You can view information to analyze workload statistics and evaluate which logical
volumes might be candidates for Easy Tier management. If you have not installed
and enabled the Easy Tier feature, you can use the performance statistics gathered
by the monitoring process to help you determine whether to use Easy Tier to
enable potential performance improvements in your storage environment.
Easy Tier considerations and limitations
This section discusses Easy Tier data relocation considerations and limitations.
Migration considerations
The following information might be helpful in using Easy Tier with the DS8000:
v You cannot initiate a volume migration on a volume that is in the process of
being migrated. The first migration must complete first.
v
You cannot initiate, pause, resume, or cancel migration on selected volumes that
are aliases or virtual volumes.
v
You cannot migrate volumes from one extent pool to another or change the
extent allocation method unless the Easy Tier feature is installed on the DS8000.
v There are likely to be a limited number of SSD arrays due to their cost. If there
are volumes that require static extent allocations on SSD arrays, one or more
homogeneous extent pools must be configured with one or more SSD ranks. If
there are volumes that require Easy Tier automatic mode, one or more
heterogeneous extent pools must be configured with one or more SSD ranks.
There is no way to share SSD ranks between storage pools. Therefore, a hybrid
pool and a non-hybrid pool cannot share space on an SSD rank.
v
Volume migration is supported for standard, auxiliary, and ESE volumes.
v If you specify a different extent allocation method for a volume, the new extent
allocation method takes effect immediately.
v A volume that is being migrated cannot be expanded and a volume that is being
expanded cannot be migrated.
v
When a volume is migrated out of an extent pool that is managed with Easy
Tier, or when Easy Tier is no longer installed, the DS8700 disables Easy Tier and
no longer automatically relocates high activity I/O data on that volume between
storage devices.
Limitations
The following limitations apply to the use of Easy Tier for DS8700 and DS8800:
v TSE logical volumes do not support extent migration. This means these entities
do not support Easy Tier manual mode or Easy Tier automatic mode.
v You cannot merge two extent pools:
– If both extent pools contain TSE volumes.
– If there are TSE volumes on the SSD ranks.
– If you have selected an extent pool that contains volumes that are being
migrated.
Chapter 3. Data management features
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