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Date: Tue, 22 May 2012 13:57:10 -0400
From: Stuart D Gathman <stuart@bmsi.com>
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Subject: Re: [linux-lvm] Fun and games with mirroring
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Long ago, Nostradamus foresaw that on 05/22/2012 10:50 AM, Vic would write:
> p.s. The reason I want to do this with LVM mirrors rather than MD RAID is
> that this is potentially a very useful way of grabbing a backup snapshot
> of a machine prior to some risky operation - it allows me to "fork" a
> machine onto two sets of media. But if it leaves the result unbootable,
> that's something of a problem...
>
LVM RAID is mainly used for pvmove at the moment.  LVM has a ways to go 
to match ZFS or AIX in LVM mirroring features.   MD RAID takes a 
snapshot just fine.  Add the mirror with mdadm, sync it, and "fail" the 
mirror and remove it before physically removing the drive.  I can see 
the issue with multiple PVs, however.  There is no atomic way to fail 
multiple mirrors at once.