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Re: [linux-lvm] Disk Died - Ideas?




-- Andreas Dilger <adilger turbolabs com>


On Sep 27, 2001 09:40 -0500, Steven Lembark wrote:
<broken record>

boot once.

vgexport /dev/vgwhatever;
vgimport /dev/vgwhatever <list of drives that didn't croak>

you will now have your VG back on line with whatever portion of the
data is no the clean drives.  any LV's spanning the dead drive are
likely to be lost anyway.  It'll take you less time to vgextend the
imported group onto a new, working drive an recover backups onto
new LV's than almost anything else you can try.

</broken record>

bzzzt. This _may_ work on HPUX and AIX, but I _highly_ doubt it will work with Linux LVM. The Linux LVM code requires that all of the disks be present, and that they all have the correct data (no metadata backups yet). You could hack the vgscan code so that it doesn't require this, but it would probably end up causing grief somewhere else before you could actually read from the LV.

AFAIK, not even HPUX or AIX would allow you to read from a partial LV
(which is the situation we are discussing here), so it wouldn't help.
What _would_ be very useful is a tool that reads the LVM metadata
directly, creates a list of available LEs (in order) and dumps them
to a file, writing zeros for LEs that are not available (and writing
large warnings for each missing LE).

Hmmm... this is what I've used repeatedly to get drives back when LVM croaks on me and doesn't like the VG's. None of the commercial LVM products allow reading from partial LV's. Point I made was that it's usually simpler to give up, get the volumes back on line, vgextend onto working PV's and restore from backup. Main problem with anything that reads partial LV's is that you can only recover raw data, which will normally leave you with a badly scrambled file system (e.g., ext2) rather than any kind of real "data" you can manage -- unless you're into locating inodes and extracting the block information then trying to jigsaw that out of the LV recovery data.

--
Steven Lembark                                               2930 W. Palmer
Workhorse Computing                                       Chicago, IL 60647
                                                           +1 800 762 1582



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