[linux-lvm] Problem with partially activate logical volume

[Zdenek Kabelac]

Dne 03. 08. 22 v 23:31 Ken Bass napsal(a):
> 
> That's pretty much it. Whenever any app attempts to read a block from the 
> missing drive, I get the "Buffer I/O error" message. So, even though my 
> recovery apps can scan the LV, marking blocks on the last drive as 
> missing/unknown/etc., they can't display any recovered data - which I know 
> does exist. Looking at raw data from the apps' scans, I can see directory 
> entries, as well as files. I'm sure the inodes and bitmaps are still there for 
> some of these, I just can't really reverse engineer and follow them through. 
> But isn't that what the apps are supposed to do?

As mentioned by my previous email you shall *NOT* fix the partially activated 
device in-place - this will not lead to good result.

User should copy the content to some valid storage device with the same size 
as he tries to recover.

You can 'partially' activate device with  "zero"  filler instead of "error" 
(see the  lvm.conf setting:     missing_stripe_filler="...") - this way you 
will just 'read' zero for missing parts.

Your another 2nd. option is to 'correct' the VG by filling  missing PV with a 
new one with preferable zeroed content - so you will not read 'random' garbage 
in places this new PV will fill the space after your missing PV.
Although even in this case - I'd still run  'fsck' on the snapshot created on 
top of such LV to give you another chance of recovery if you will pick a wrong 
answer  (since fsck might be 'quite' interactive when doing such large-scale 
repair)


> Sorry I haven't replied sooner, but it takes a long time (days) to clone, then 
> scan 16Tb...
> 
> So, please any suggestions are greatly appreciated, as well as needed.
> 
> ken
> 
> (I know: No backup; got burned; it hurts; and I will now always have backups. 
> 'Nuf said.)

Before you run your 'fsck' create a snapshot of your newly created 'backup' 
and make all the repair actions in the snapshots.

Once you are 'satisfied' with 'repaired'  filesystem you can then 'merge' 
snapshot back to your origin and use it.

Regards

Zdenek