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From: Chris Murphy <lists@colorremedies.com>
To: Paul Monsour <boulos@gmx.com>
Cc: Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: dd does it again!
Date: Mon, 11 Nov 2019 19:19:10 +0000
Message-ID: <CAJCQCtToDnDCpTrERudijavs2Vho2-hgeipHEJG90=D_53DXvQ@mail.gmail.com> (raw)
In-Reply-To: <trinity-9b5e3549-dd52-48e7-98f1-9f8bfd1a358a-1573440280042@3c-app-mailcom-bs04>

On Mon, Nov 11, 2019 at 2:44 AM Paul Monsour <boulos@gmx.com> wrote:
>
> parted -l produced:
>
> Model: ATA ST3000DM008-2DM1 (scsi)
> Disk /dev/sdc: 3001GB
> Sector size (logical/physical): 512B/4096B
> Partition Table: gpt
> Disk Flags:
> Number  Start   End     Size    File system  Name  Flags
>  1      1049kB  3001GB  3001GB  btrfs        Home
>
> Model: ATA ST3000DM008-2DM1 (scsi)
> Disk /dev/sdd: 3001GB
> Sector size (logical/physical): 512B/4096B
> Partition Table: msdos
> Disk Flags:
> Number  Start  End     Size    Type     File system  Flags
>  2      119kB  1593kB  1475kB  primary               esp
>
> The portion of the dd command that wrecked the files was "of=/dev/sdd1"

OK? According to the parted output, there is a single partition number
2, therefore only /dev/sdd2 should exist and the dd command should
have failed. So... something is missing in the information provided,
or maybe a typo somewhere.



>
> btrfs restore produced just:
>
> drwxr-xr-x 1 root root   0 Nov 10 12:43 ftp
> drwxr-xr-x 1 root root 362 Nov 10 12:51 palsor
>
> However, I was (perhaps optimistically) heartened by what "btrfs-find-root /dev/sdc1" produced:
>
> # btrfs-find-root /dev/sdc1
> warning, device 2 is missing
> Superblock thinks the generation is 322292
> Superblock thinks the level is 1
> Found tree root at 649710272512 gen 322292 level 1
>
> How do I use this information? Is there reason to be optimistic?

No. The best possible case is data raid0, and metadata raid1, in which
case the file system will mount with "degraded" option and you'll be
able to recover any files that are completely on the intact device,
and not subject to any striping. Otherwise they will be considered by
Btrfs to be corrupt/missing, although I'm not sure if it results in
EIO or something else. If metadata is also raid0, then the file system
won't mount. You probably also won't have much success with btrfs
restore either.


-- 
Chris Murphy

      parent reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-11  2:44 Paul Monsour
2019-11-11  5:19 ` Anand Jain
2019-11-11 19:19 ` Chris Murphy [this message]

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