Re: Scrub aborts due to corrupt leaf

From: Chris Murphy <lists@colorremedies.com>
To: Larkin Lowrey <llowrey@nuclearwinter.com>
Cc: "Hans van Kranenburg" <Hans.van.Kranenburg@mendix.com>,
	"Chris Murphy" <lists@colorremedies.com>,
	"Holger Hoffstätte" <holger@applied-asynchrony.com>,
	"Qu Wenruo" <quwenruo.btrfs@gmx.com>,
	"Btrfs BTRFS" <linux-btrfs@vger.kernel.org>
Subject: Re: Scrub aborts due to corrupt leaf
Date: Wed, 10 Oct 2018 20:51:01 -0600	[thread overview]
Message-ID: <CAJCQCtSbLkpYnwEO05D5R2oXVznJ3KwBxjyfBDnM4PaGwSXUhg@mail.gmail.com> (raw)
In-Reply-To: <9e6b268b-b545-bad1-f33a-b29ea1af7db0@nuclearwinter.com>

On Wed, Oct 10, 2018 at 8:12 PM, Larkin Lowrey
<llowrey@nuclearwinter.com> wrote:
> On 10/10/2018 7:55 PM, Hans van Kranenburg wrote:
>>
>> On 10/10/2018 07:44 PM, Chris Murphy wrote:
>>>
>>>
>>> I'm pretty sure you have to umount, and then clear the space_cache
>>> with 'btrfs check --clear-space-cache=v1' and then do a one time mount
>>> with -o space_cache=v2.
>>
>> The --clear-space-cache=v1 is optional, but recommended, if you are
>> someone who do not likes to keep accumulated cruft.
>>
>> The v2 mount (rw mount!!!) does not remove the v1 cache. If you just
>> mount with v2, the v1 data keeps being there, doing nothing any more.
>
>
> Theoretically I have the v2 space_cache enabled. After a clean umount...
>
> # mount -onospace_cache /backups
> [  391.243175] BTRFS info (device dm-3): disabling free space tree
> [  391.249213] BTRFS error (device dm-3): cannot disable free space tree
> [  391.255884] BTRFS error (device dm-3): open_ctree failed

"free space tree" is the v2 space cache, and once enabled it cannot be
disabled with nospace_cache mount option. If you want to run with
nospace_cache you'll need to clear it.

>
> # mount -ospace_cache=v1 /backups/
> mount: /backups: wrong fs type, bad option, bad superblock on
> /dev/mapper/Cached-Backups, missing codepage or helper program, or other
> error
> [  983.501874] BTRFS info (device dm-3): enabling disk space caching
> [  983.508052] BTRFS error (device dm-3): cannot disable free space tree
> [  983.514633] BTRFS error (device dm-3): open_ctree failed

You cannot go back and forth between v1 and v2. Once v2 is enabled,
it's always used regardless of any mount option. You'll need to use
btrfs check to clear the v2 cache if you want to use v1 cache.

>
> # btrfs check --clear-space-cache v1 /dev/Cached/Backups
> Opening filesystem to check...
> couldn't open RDWR because of unsupported option features (3).
> ERROR: cannot open file system

You're missing the '=' symbol for the clear option, that's why it fails.

-- 
Chris Murphy