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[ale] Kubuntu 13.04 danger: beware /dev/dm-*

Sorry to hear about this. UUIDs suck to work with (too long for normal
short term memory - too non-associative for long-term memory) but they as
certainly stable and definitive.

On Tue, Apr 30, 2013 at 8:42 PM, George Allen <glallen01 at gmail.com> wrote:

> So, I just finished recovering from a data-loss causing error in the new
> ubuntu:
> I had one hard drive with 12.10, and a new one with a fresh install of
> 13.04.
> Both used LVM, with slightly different custom setups...
> In transferring the files from the old to new drives, via rsync and an
> external usb adapter, the transfer suddenly errored out after several
> GBs.
> I don't have the logs handy to give better notes (specific errors),
> but basically:
> - sometime late in the rsync the computer decided to write something to
> swap.
> - 13.04 had created the cryptswap device using /dev/dm-3 instead of
> /dev/mapper/vg-swap or a UUID (in /etc/crypttab)
> - sometime in my modifying the partitions/lvm and adding a usb drive
> that also contained lvm volumes, /dev/dm-* were re-numbered
> So as soon as the computer touched swap, it corrupted my /dev/vg/home
> logical volume
> It took me a while to figure out what was going on... then with blkid
> and lots of googling I managed to find out by comparing UUIDs for each
> device.
> To avoid further problems - grep -rE '/dev/(sd.|mapper|disk|dm)' * on
> both systems confirmed that '/etc/crypttab' on the 13.04 install was
> the only important file that referenced anything by dm-* but that one
> file can hose your system if somehow dmsetup renumbers things after
> changes.
> -George
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James P. Kinney III
*Every time you stop a school, you will have to build a jail. What you gain
at one end you lose at the other. It's like feeding a dog on his own tail.
It won't fatten the dog.
- Speech 11/23/1900 Mark Twain
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