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[linux-lvm] lvm2 *TEMPORARY* PV failure - what happens?



I've been intrigued by the discussion of what happens when a PV fails, and have begun to wonder what would happen in the case of a transient failure of a PV.

The design I'm thinking of is a SAN environment with several multi-terabyte iSCSI arrays as PVs, being grouped together into a single VG, and then carving LVs out of that. We plan on using the CLVM tools to fit into a clustered environment. The arrays themselves are robust (RAID 5/6, redundant power supplies, etc.) and I grant that if we lose the actual array (for example, if multiple disks fail), then we are in the situation of a true and possibly total failure of the PV and loss of it's data blocks.

But there is always the possiblity that we could lose the CPU, memory, bus, etc. in the iSCSI controller portion of the array, which will cause downtime, but no true loss of data. Or someone may hit the wrong power switch and just reboot the thing, taking it offline for a short time. Yes, that someone would probably be me. Shame on me.

The key point is that the iSCSI disk will come back in a few minutes/hours/days depending on the failure type, and all blocks will be intact when it comes back up. I suppose the analagous situation would be using LVM on a group of hot swap drives and pulling one of the disks, waiting a while, and then re-inserting it.

Can someone please walk me through the resulting steps that would happen within LVM2 (or a GFS filesystem on top of that LV) in this situation?

Thanks,

-Ty!

--
-===========================-
 Ty! Boyack
 NREL Unix Network Manager
 ty nrel colostate edu
 (970) 491-1186
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