Multipathing on HP-UX (LVM vs. VxVM)

A few versions back, HP started including Veritas VxVM (Veritas Volume Manager) with HP-UX 11i. There was some consternation that VxVM was a third-party non-HP product, and that it would mean the demise of LVM.

However, now in HP-UX 11i v3 HP has turned the tables on Veritas (now Symantec) so to speak. In essence, this is another replay of the operating system vendor shooting down the third-party vendor.

In the past, HP-UX did not support load balancing on HP-UX with the native LVM disks; only VxVM supported multipathing with fail-over and load balancing. Now, in HP-UX 11i v3, the native drivers support full load balancing and failover with multipathing, and VxVM has been eviscerated: under 11i v3, VxVM’s multipathing DMP is put into straight-through mode (that is, no failover, no load balancing) and the new 11i native multipathing takes over.

When the disks are presented to HP-UX 11i v3 properly, the following will be output for the ioscan -m dsf command:

# ioscan -m dsf
Persistent DSF           Legacy DSF(s)
/dev/rdisk/disk16        /dev/rdsk/c7t0d0
/dev/rdisk/disk17        /dev/rdsk/c7t0d1
/dev/rdisk/disk18        /dev/rdsk/c7t0d2
/dev/rdisk/disk19        /dev/rdsk/c7t0d3
/dev/rdisk/disk20        /dev/rdsk/c7t0d4

With the proper multipathing in place, the “persistent DSFs” (DSFs are Device Special Files) are matched to multiple paths (which are reflected in the legacy DSFs). If you see this output from ioscan -m dsf, then multipathing is enabled for the disks as shown.

If ioscan -m dsf reports a syntax error, then you are not running on HP-UX 11i v3 – 11i v2 and below did not support the -m option.

It would appear that HP was serious about supporting LVM on HP-UX after all.