Re: [linux-lvm] Problem with partially activate logical volume

[Ken Bass <daytooner@gmail.com>]

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Zdenek: thanks. That makes more sense. I will try after (re-)cloning. Give it  a day or so. 

Ken 


On Aug 5, 2022, 7:03 AM, at 7:03 AM, Zdenek Kabelac <zdenek.kabelac@gmail.com> wrote:
>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

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