[gentoo-amd64] Re: LVM2 Failures

[Duncan]

Richard Freeman <rich@××××××××××××××.net> posted
45EC04D0.3030505@××××××××××××××.net, excerpted below, on  Mon, 05 Mar 2007
06:53:52 -0500:

> Does anybody know what happens if an LVM2 physical volume fails?
> Obviously any data on that physical volume is lost, and I'd imagine any
> logical volumes that reside in part or whole on that physical volume
> would be a mess.
>
> What happens to logical volumes in the same volume group which do not
> reside on the lost physical volume?  Are they easily recovered?  How
> about logical volumes in a different volume group - are those affected
> at all?  I didn't see any documentation on this topic on the lvm2 HOWTO.
>
> I'm contemplating adding another drive and rsyncing stuff to it. Ideally
> I'd like to use lvm2 with the new drive, and just make sure the stuff
> that is important to backup doesn't end up on the same physical drive
> (easy enough to do).  However, I don't want the backup drive to
> disappear in a puff of logic if one of the main drives fails.

In addition to BSSJ's answer, since you are just setting up, I'd suggest 
paying particular attention to the LVM metadata sets.  It gives you a lot 
of control as to how many copies it makes and where it puts them, so just 
make sure it's saving its metadata say once or twice to each of several 
of the drives (of course NOT as files on the LVs themselves!) you 
mentioned you had in your collection, so you'll be sure and have it 
around to recover with if there's anything at all left to recover.  It'd 
suck to know what you needed was there and fine, but unavailable because 
all the metadata needed to reconstruct what was left of the volumes was 
on the drives that failed!

Here (altho my LVM is layered over RAID-6), I tweaked both the number of 
backups, and the size of the history, thus providing me rather more of a 
redundancy safety margin, just in case.

You'll also want to keep redundant copies of the recovery tools around, 
as all that metadata won't do a lot of good if LVM isn't loading it and 
you can't tell why because the recovery tools are either on the LVM 
themselves, or were lost with the drive(s) that went out.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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