linux-ext4 - Re: Recover from a "deleted inode referenced" situation

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Message-ID: <CAJz=VjF_BGVuCrhDbQA7H3nwVLVF2PyWppwCe5mV6DDPAZ6UWQ@mail.gmail.com>
Date:   Tue, 17 Oct 2017 08:32:52 -0700
From:   Kilian Cavalotti <kilian.cavalotti.work@...il.com>
To:     "Theodore Ts'o" <tytso@....edu>
Cc:     Andreas Dilger <adilger@...ger.ca>, linux-ext4@...r.kernel.org
Subject: Re: Recover from a "deleted inode referenced" situation

On Sun, Oct 15, 2017 at 6:28 PM, Theodore Ts'o <tytso@....edu> wrote:
>> Is there any possibility that the filesystem could appear to be
>> resized (extended) with the actual inode table still referencing the
>> pre-resize one?
>
> It's possible, I suppose.  If the vendor script unmounted the file
> system and then attempted to run e2fsck -fy to fix the file system,
> perhaps.  In which case the damage could also have been done by the
> e2fsck -fy run, depending on how badly the file system was corrupted
> before this whole procedure was started.

In that case, is there any way to re-shrink the filesystem to its
pre-expansion size, and try to read the pre-expansion inode table from
another superblock? Or did the r/w remount over-write all the existing
superblocks with the same new, corrupted information?

> But that would imply that the NAS box would have to stop serving the
> file system, and it would have been pretty obviously an off-line
> procedure.

Well, I have this elements that point in that direction:
1. the online resize2fs tentative aborted (I have that logged),
2. the filesystem has been expanded (I can see it now),
3. it definitely stopped serving the filesystem at some point.

Cheers,
-- 
Kilian