HP StorageWorks XP Remote Web Console Software - Manual (Page 14)

Maximizing Your Compatible PAV Results
To maximize your results from Compatible PAV operations, be aware of the following:
•
For Compatible PAV
The best results can be obtained if the number of aliases per LCU image is equal to the
number of available channel paths minus one. If the number of aliases is specified this
way, I/O operations can use all channel paths, thus providing the best results. ◦
◦ The unused device addresses in the storage system are used as alias devices. If you use
most of the unused device addresses for aliases, you will only have a small amount of
free devices available. If you determine that a large number of aliases will be required,
consider creating more LCU's to ensure that storage will be available when needed.
◦ Compatible PAV may not provide good results for devices that are always shared and
used by multiple host systems. For access by multiple hosts, you should use the Multiple
Allegiance (MA) host software function supported by the storage system.
◦ Up to 255 alias devices can be assigned to one base device. In this case, however, the
desired effect will not be achieved because I/O conflict can occur with the base device
and the alias devices; therefore, the devices may be unable to receive the I/Os (as there
will be a high chance the same physical tracks will be addressed).
For dynamic Compatible PAV
◦ If dynamic Compatible PAV can be used in all systems, good results can be expected if
you assign eight to sixteen (8-16) aliases to each LCU image.
For static Compatible PAV
◦ The recommended ratio of base devices to alias devices is 1:3. Table 2 (page 14) shows
examples of calculating the number of base and alias devices for an LCU image with
256 devices. If you know the types of jobs and/or the expected host access rates for the
base devices, you should determine the number of aliases for each base device to meet
your requirements for each base device.
Table 2 Ratio of Base Devices to Alias Devices
Total Devices Number of Alias Devices Number of Base Devices Ratio (base devices : alias devices)
256 (64+192) 192 64 1:3 (recommended)
256 (85+171) 171 (85+86) 85 1:2
256 (128+128) 128 128 1:1
•
For XP Compatible Hyper PAV
◦ When using XP Compatible Hyper PAV, assign eight to sixteen (8-16) aliases to each
LCU image for best performance. Based on your system, determine the quantity of aliases
required for best performance: not too many so that I/O is impacted or so few that their
usefulness is limited.
◦ During assignment of aliases to base devices in Remote Web Console, do not assign
more than three aliases to a single base device address.
◦ The number of alias devices assigned to each base device should be kept as equal as
possible. For example, a LCU with 10 aliases could have three aliases each assigned to
the first to third base addresses, one alias to the fourth base address, and no alias
assignments to the remaining base addresses or you could assign one alias to each of
the 10 addresses, as needed.
14 About Compatible PAV Operations