[linux-lvm] lvm2 *TEMPORARY* PV failure - what happens?
Ming Zhang
mingz at ele.uri.edu
Tue Apr 25 19:57:29 UTC 2006
my 2c. fix me if i am wrong
either activate the VG partially, and then all LVs on other PVs are
still accessible. I remember these LVs will only have RO access. Though
I have no idea why.
use dm-zero to generate a fake PVs and add to VG, then allow VG to
activate and access those LV. But i do not know if you access a LV that
is partially or fully on this PV, what will happen.
Ming
On Tue, 2006-04-25 at 13:08 -0600, Ty! Boyack wrote:
> 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!
>
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