HP XP P9500 Storage - Manual (Page 12)

When to use fixed-sized provisioning
Fixed-sized provisioning is a best fit in the following scenarios:
•
Use fixed-size provisioning in cases where standard IBM 3390 volume sizes (3390-3, 3390-9,
etc.) are required.
Custom-sized provisioning
Custom-sized (or variable-sized) provisioning has more flexibility than fixed-sized provisioning and
is the traditional storage-based volume management strategy typically used to organize storage
space.
To create custom-sized volumes on a storage system, an administrator creates volumes of the
desired size from individual array groups. These volumes are then individually mapped to an
address composed of a control unit and logical device within the control unit.
Following are three scenarios where custom-sized provisioning is an advantage:
•
In fixed-sized provisioning, when several frequently accessed data sets are located on the
same volume, users accessing other data sets on the same volume may encounter increased
response time because of logical device contention. If the custom-sized feature is used to divide
the volume into several smaller volumes and I/O workload is balanced (each data set is
allocated to a different volume), then access contention is reduced and performance is
improved.
•
In fixed-sized provisioning, not all of the capacity may be used. Unused capacity on the volume
will remain inaccessible to other users. If the custom-sized feature is used, smaller volumes
can be created that do not waste capacity.
•
Applications that require the capacity of many fixed-sized volumes can instead be given fewer
large volumes to relieve device addressing constraints.
To change the size of a volume already in use, you first create a new volume larger than the old
one, and then move the contents of the old volume to the new one. The new volume must be
configured in the IOGEN on the server. Depending on how the data was copied (for example
using software such as TDMF, or internal capability such as FlashCopy) the old device may need
to be varied offline and the new device varied online. This assumes that the source and target
devices are already gen'ed into the mainframe IO configuration.
A disadvantage is that this manual intervention can become costly and tedious and this provisioning
strategy is appropriate only in certain scenarios.
When to use custom-sized provisioning
Use custom-sized provisioning when you want to manually control and monitor your storage
resources and usage scenarios.
Basic provisioning workflow
The following illustrates the basic provisioning workflow:
12 Introduction to provisioning