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/rdsk/c6t0d0
/dev/rdisk/disk17        /dev/rdsk/c7t0d1
                         /dev/rdsk/c6t0d1
/dev/rdisk/disk18        /dev/rdsk/c7t0d2
                         /dev/rdsk/c6t0d2
/dev/rdisk/disk19        /dev/rdsk/c7t0d3
                         /dev/rdsk/c6t0d3
/dev/rdisk/disk20        /dev/rdsk/c7t0d4
                         /dev/rdsk/c6t0d4

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.

9 thoughts on “Multipathing on HP-UX (LVM vs. VxVM)”

    1. Neither HP-UX 11i v3 native multipathing nor 11i v2 PVLinks require additional licenses; they are part of the system.

      However, if you want to “load balance” or spread the I/O around on 11i v2 or older, then you need a third-party solution.

  1. Mmm. I wouldn’t say that there was no multipathing outside of veritas before 11.31. HP had two SecurePath and AutoPath. They were originally seperate but eventually just became SecurePath. And though 11.31 multipathing is nice, I still like vxvm and vxdmp better.

    1. I hope I didn’t say that; what I was saying is that there is no distributed I/O as part of the base HP-UX system before 11.31.

      There were (and are) commercial offerings that do this (as you pointed out), but with HP-UX 11.31 it is built into the operating system itself with the new I/O subsystem.

  2. Just to clarify something in your post. You can turn off nMPs ability to multipath with the new Agile I/O Mass storage stack. DMP can multipath using the Agile DSFs instead of just a straight through mode as described in your post.

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