[Linux-cluster] Get qdisk to use /dev/mapper/mpathx devices instead of /dev/dm-x

[Celso K. Webber]

Hello,


----- Original Message ----
From: Charlie Brady <charlieb-linux-cluster at budge.apana.org.au>

> Your qdisk label should be unique, and you should be controlling 
> visibility of qdisks.

I think you did not understand what I meant. If you have multiple devices pointing to the same LUN (this happens with many multipathing software), your OS will end up with various block devices in /dev pointing to the same LUN, thus making qdiskd to pick up the first one it founds, and ignoring the rest. If it not picks the right one, you'll have no reason to have multipath connections to your shared storage. So its obvious that my disk label is unique, the problem is when you have multiple devices pointing to it.

> Another case is when the device is not found at all, this 
> happened to me before.

>> If that happens, you have a bigger problem than just using the qdisk label 
>> to identify the qdisk, don't you?

No, I don't agree. I had a very recent situation with a RHEL 5.3 AP installation, EMC CX series storage (Clariion), PowerPath multipathing software, where the qdiskd simply didn't recognize the /dev devices associated to the quorum disk LUN. It simply didn't initialize because didn't find the label on any device it scanned. Simply pointing it to the correct PowerPath pseudo device, /dev/emcpowerq in this case, solved the problem.

Again, I'm not discussing specific situations using Linux DM multipathing software, but other solutions such as EMC's PowerPath.

And I'm sure I have enough experience with that, working for more than 5 years on field implementations for Dell.

My intention was to add experience, for me the best option is ALWAYS to use the device you want. Even with Linux DM Multipath devices.

thank you.

Regards, Celso.