Defining Devices; Unused Device Addresses Usage As Alias Devices; Optimal Parallel Access Volumes Results And Base-To-Alias Device Ratios; Optimal Dynamic Pav Results And Alias Devices - HPE XP7 User Manual

Defining devices

Unused device addresses usage as alias devices

You can use unused device addresses in a CU as aliases for base devices. An optimum base-to-alias
device ratio ensures maximum efficiency in processing I/O requests.
Determining an optimum ratio depends on the type of PAV being used as well as the I/O rate for the
individual base devices. While some ratios are suggested, the best method is to use a tool that analyzes
your RMF data and recommends the appropriate number of aliases to configure for a base address. The
best tools will make recommendations for each type of PAV (static, dynamic, and HPAV).

Optimal Parallel Access Volumes results and base-to-alias device ratios

A ratio of 1:3 is recommended as a starting point for each base when using static PAV.
NOTE: The optimal device ratio will vary based on how often a base device is accessed by the host
system.
For example, if you define all 256 devices of a CU to the host system, 64 base devices and 192 alias
devices would exist. Three alias devices could be assigned to each base device.

Optimal dynamic PAV results and alias devices

Since dynamic PAV will change alias assignments, it is recommended that you start with a ratio of 1:1 for
a CU.
NOTE: If multiple host systems access devices, you can experience less than optimal results. In this
case, use Multiple Allegiance (MA) host software.

Hyper Parallel Access Volumes optimum base/alias device ratio

For HPAV, HPE recommends between 16 and 32 alias devices in a CU. These devices can be assigned
to a single base devices when performing configuration using Remote Web Console. All the aliases in a
CU will be placed in a pool and used as required for any base devices.

Compatible Super PAV optimum base/alias device ratio

As with HPAV, using 16 to 32 alias devices in a CU is also recommended for Super PAV.
The Super PAV feature uses alias devices in a CU where the base device belongs first as long as they
have enough space. Throughput performance improvement using Super PAV can be expected when the
number of used alias devices in a CU varies, and when CUs where few alias devices are used and CUs
where they run out are contained in an AMG. On the other hand, when alias devices are sufficient, effect
of using Super PAV might not be expected.
The methods for defining alias devices using Remote Web Console for HPAV and for Super PAV are the
same. Defined alias devices are grouped into an AMG containing even numbered CUs and into an AMG
containing odd numbered CUs. Base devices can use only alias devices in an AMG to which alias
devices in the local CU belongs. Therefore, balance the number of used alias devices across even
numbered CUs or odd numbered CUs.
Defining devices 19