Disk Recovery Part III

[Matthew Gillen]

Derek Atkins wrote:
> IMNSHO, avoid LVM like the plague..  I've personally had nothing but
> problems with LVM.  

Thought I'd throw my $0.02 in on LVM:
Unless you're running raid-1 under LVM, with a 2-disk LVM you're
doubling your chances of an unrecoverable error.  LVM lets the
filesystem act like it's operating on a single device, and therefore if
one disk fails, you'll have a heck of a time getting data off the
surviving disk (I'd say fully 80% of the traffic on the lvm mailing list
is dealing with this issue).  The LVM FAQ (if there is such a thing)
should say this in big letters: LVM by itself is not tolerant of
physical device failures.  I can't believe the people who LVM 8 disks
together with no backup, have a failure, then expect that they can
salvage their data off the 7 disks that are still good...

The obvious solution is to use RAID-1/5 devices as your physical devices
that LVM builds on.  This works very well for me (note for Fedora users,
and perhaps others: SoftwareRAID+LVM+XFS is very problematic at the
moment, use any other filesystem instead).

So here's what I do: I have four disks; two sets of RAID-1 mirrors.  The
bigger set of disks have a few partitions, all RAID'd with each other.
I don't bother making / on LVM: if I ever get to the point where / needs
more than 10GB I'll probably be needing to do major changes anyway.

/home is where I keep all the fun (big) stuff, so that was built on an
LVM.  The remainder of the big disks (RAID'd together) are one
'physical' device, and my other disk set (RAID'd together) form the
other 'physical' device.

--Matt