06-16-2013 08:09 AM
What I met early today was beyond my understanding of LVM or io sub-system of HP-UX.
superdome servers with HP-UX 11.11, connected to SAN switches to access EMC storage, assuming that dsf of LUNs in EMC storage were c21t*d* & c22t*d*. SAN switches were replaced, which I was not informed. Of course things were not ok last night and both servers rebooted. ioscan output shows that dsfs of LUNs in EMC storage are now c17t*d* & c18t*d*. There was no vg manipulation last night, no map file saved, so I was hopeless when I finally run into this issue.
BUT, I COULD ACTIVATED ALL VGS USING vgchange -a y! And vgdisplay show pv name of all these vgs were c21t*d* & c22t*d*, which I assume no longer existed in OS. vgexport and vgimport were OK so it was easy to produce good configuration.
I don't understand it, any one does? there is powerpath on both servers.
06-17-2013 01:33 AM - edited 06-17-2013 01:47 AM
That's PowerPath at work.
It remembers the device names each LUN was associated with, and allows the system to use even the "dead" DSFs, if the system has at least one good path to the LUN. This is because PowerPath takes the traffic from any and all DSFs for a particular LUN, and load balances the traffic across all the good paths for that LUN. You just saw an extreme case of that.
By the way, a map file can be generated with just the information in /etc/lvmtab, so it's no problem to export a VG whose disks are not accessible. This is a basic HP-UX LVM feature.
In fact, if you have disconnected some disks before removing/exporting their VG configuration from the OS side, exporting the now-inaccessible VG is the only clean way to get rid of the remains of their configuration.
Edit: as you've now updated the VG configuration, you probably should now run "powermt check" and clean up the old dead paths from the PowerPath configuration too.
I recall my first surprise with PowerPath was exactly like your situation too. I looked at the ioscan and LVM configuration, thought "that does not make sense", then looked at PowerPath configuration, noticed that it was tracking both the old & new DSFs, and thought "Could that be it???" Some furious RTFMing later, my conclusion was: "Huh. Looks like that's exactly it. The PowerPath sure does quite a bit of work behind HP-UX's back."
06-17-2013 05:35 AM
Thank you for your reply!
"a map file can be generated with just the information in /etc/lvmtab", I never try this, how to get that?