[gpfsug-discuss] Multipath configurations
jonathan at buzzard.me.uk
Thu Sep 19 16:38:05 BST 2013
On Thu, 2013-09-19 at 15:53 +0100, Orlando Richards wrote:
> Along the way we discovered an odd GPFS "feature" - if some nodes in the
> cluster use RDAC (and thus have /dev/sdXX devices) and some use
> multipathd (and thus use /dev/dm-XX devices), then the nodes can either
> fail to find attached NSD devices (in the case of the RDAC host where
> the NSD's were initially created on a multipath host) or can try to talk
> to them down the wrong device (for instance - talking to /dev/sdXX
> rather than /dev/dm-XX). We just set up this mixed environment to
> compare rdac vs dm-multipath, and don't expect to put it into production
> - but it's the kind of thing which could end up cropping up in a system
> migrating from RDAC to dm-multipath, or vice versa. It seems that on
> creation, the nsd is tagged somewhere as either "dmm" (dm-multipath) or
> "generic" (rdac), and servers using one type can't see the other.
That is all covered in the GPFS documentation under "don't do that" ;-)
> Thankfully, we have no plans to mix the environment - but for future
> reference it could be important (if ever migrating existing systems from
> rdac to dm-multipath, for instance).
The recommendation is roughly umount GPFS everywhere, export the file
system, change everything to dm-multipath/RDAC depending on your poison,
import file system and mount again. I think you can skip the
export/import by doing some fiddling to switch the NSD type.
Jonathan A. Buzzard Email: jonathan (at) buzzard.me.uk
Fife, United Kingdom.
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