linux-ext4 - Re: Filesystem size problem.

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Message-ID: <CAEUYfyN373=Eacbu=jL-YPfcmLC0VjvMc++__eVUAJb++gq6Ug@mail.gmail.com>
Date:   Mon, 12 Dec 2016 18:48:44 -0800
From:   Simon Matthews <simon.d.matthews@...il.com>
To:     linux-ext4@...r.kernel.org
Subject: Re: Filesystem size problem.

On Mon, Dec 12, 2016 at 2:36 PM, Andreas Dilger <adilger@...ger.ca> wrote:
> On Dec 9, 2016, at 9:35 PM, Eric Sandeen <sandeen@...hat.com> wrote:
>>
>> On 12/9/16 2:29 PM, Andreas Dilger wrote:
>>> On Dec 8, 2016, at 10:40 PM, Simon Matthews <simon.d.matthews@...il.com> wrote:
>>>>
>>>> I have an ext3 filesystem that will not mount under newer versions of
>>>> the kernel and I hope someone here can help.
>>>>
>>>> Obviously, one solution is "backup and re-create from scratch". I have
>>>> the backups, but I hope that there may be a quicker method to fix the
>>>> issues.
>>>>
>>>> The root issue is that the filesystem is very slightly smaller than
>>>> the allocated space.
>>
>> So the device is now smaller than the filesystem thinks, right?
>>
>>> The filesystem exists on a MDRAID device and I
>>>> think that when I converted the MDRAID to a newer metadata version, it
>>>> truncated the available size, slightly. However, how I got here isn't
>>>> really important, fixing it now is.
>>>
>>> Running "e2fsck -fy" should fix this.  I'd recommend to use the latest
>>> version of e2fsck.
>>
>> Reaslly?  e2fsck can change total blocks in the superblock to accomodate a
>> shrunken device?  That's a new one for me...
>
> Strange, I thought this case was handled properly by e2fsck.
>
> You could probably fix this with:
>
> # debugfs -R "ssv blocks_count 693359326" /dev/md5



"probably"?

How safe or dangerous is this? Does the filesystem have to be unmounted first?

Simon
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