Re: [linux-lvm] rescue data after hd crash

[Graham Wood <gwood@dragonhold.org>]

On Wed, May 31, 2006 at 02:34:04PM +0200, chris wrote:
> I have create a volume group with 4 250GByte harddisks with an ext3 file  
> system on the 1TB result.
Stripe or concat?

> now the third harddisk failed and the volume group is "dead" - obviously.
The way you created the volume had no redundancy - therefore 25% of your data is gone, as 
well as the volume's "completeness".

If you did a concat, then you (with playing) may be able to get some data back from the 
first 500GB of the volume - but I wouldn't want to rely on anything that came back from it.  
I'd suggest getting hold of 2 identical blank disks, and doing a binary (dd) copy of disks 1 
and 2 to them - and then work on them.  You might be able to use vgcfg{backup,restore} to 
tell the system that this volume is actually only on 2 disks....  However, anything that 
references data > 500GB into the volume is almost definitely lost - because although you've 
got 750G-1TB, it's almost all going to be linked back into the section that you've lost.

If you did a stripe, then you can forget getting any data back off it.  You've lost every 
4th block of whatever size you striped on.  E.g. with a 64k stripe size, you'll have lost 
from 128k-192k, 384k-448k, etc. - and there's almost definitely going to be nothing 
salvagable from that.

Graham