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From: STEVE LEUNG <sjleung@shaw.ca>
To: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: corruption with multi-device btrfs + single bcache, won't mount
Date: Sun, 10 Feb 2019 22:25:51 -0700 (MST)
Message-ID: <393920696.241868146.1549862751510.JavaMail.zimbra@shaw.ca> (raw)
In-Reply-To: <e8219111-4e0d-65f4-ac06-627cebaac94a@gmx.com>



----- Original Message -----
> From: "Qu Wenruo" <quwenruo.btrfs@gmx.com>
> On 2019/2/10 下午2:56, STEVE LEUNG wrote:
>> Hi all,
>> 
>> I decided to try something a bit crazy, and try multi-device raid1 btrfs on
>> top of dm-crypt and bcache.  That is:
>> 
>>   btrfs -> dm-crypt -> bcache -> physical disks
>> 
>> I have a single cache device in front of 4 disks.  Maybe this wasn't
>> that good of an idea, because the filesystem went read-only a few
>> days after setting it up, and now it won't mount.  I'd been running
>> btrfs on top of 4 dm-crypt-ed disks for some time without any
>> problems, and only added bcache (taking one device out at a time,
>> converting it over, adding it back) recently.
>> 
> However there is a patch to address this kinda "common" corruption scenario.
> 
> https://lwn.net/Articles/777265/
> 
> In that patchset, there is a new rescue=bg_skip mount option (needs to
> be used with ro), which should allow you to access whatever you still
> have from the fs.
> 
> From other reporters, such corruption is mainly related to extent tree,
> thus data damage should be pretty small.

I can also report that this patch has allowed me to recover the data.
The devices were apparently flaky with the addition of the cache
device to the system, which explains why the filesystem got
corrupted.

Thanks very much for the help!

Steve

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-10  6:56 STEVE LEUNG
2019-02-10 10:35 ` Thiago Ramon
2019-02-11  5:22   ` STEVE LEUNG
2019-02-10 13:52 ` Qu Wenruo
2019-02-11  5:25   ` STEVE LEUNG [this message]
2019-02-12  6:22   ` Steve Leung
2019-02-12  6:51     ` Qu Wenruo

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