Maximum LUN Configuration and Considerations for HP-UX

With the September 2007 release of HP-UX 11i v3, the maximum number of “Active” and
“Open/Visible” LUN paths supported is 262144. The following patches or their superseding patches
are required to configure the same limits on the February 2007 release of HP-UX 11i v3:
• PHKL_36332: GIO cumulative path
• PHKL_36334: WSIO cumulative path
Device Maximums
In addition to the system considerations specified above, the LUN configuration of the storage device
itself must be planned both internally and with respect to the configuration/topology. Consider all of
the possible factors across the storage device, HBA, and the system in your LUN count determinations.
Review the storage device documentation for details on device-specific configurations.
Considerations
Whenever a system is configured, the number of LUNs must be properly balanced with respect to the
various I/O links and buses and with the configuration of volume manager volumes and volume
groups, the size of memory, the number of CPUs, the corresponding application workload, and so
forth. The details of system and mass storage configuration and tuning to support large LUN
configurations are beyond the scope of this paper, but a few general guidelines and specific
considerations applicable to large LUN configurations are outlined here.
Server Considerations
HP recommends that large numbers of LUNs be connected only to larger HP-UX servers such as the
rp7420/rp8420, rx7620/rx8620 and Superdome systems. Smaller servers can share in the use of
large numbers of LUNs in a cluster, but due to memory and slot limitations are generally unable to
directly support many LUNs.
Kernel Tunables
As the number of LUNs is increased, the “maxfiles” and “maxfiles_lim” kernel tunables typically also
need to be increased. Contact HP support personnel for help in tuning your specific configuration.
Volume Manager Considerations
HP-UX LVM supports a maximum of 256 volume groups with up to 255 physical volumes per volume
group. Therefore, given the original 11i v1 LUN device maximums specified in Table 1, you can
configure a system with 32 volume groups, each of which contains 128 physical volumes, for a total
of 4096 physical volumes (where a physical volume is equivalent to a LUN device). For a more well-
balanced configuration you can spread the physical volumes across a larger number of volume
groups: for example, a configuration with 64 volume groups with 64 physical volumes per volume
group for 4096 total physical volumes.
In releases prior to HP-UX 11i v3, LVM has a “maxvgs” tunable, which restricts the overall number of
volume groups which can be configured. It defaults to 10. To enable larger configurations, increase
this tunable.
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