Re: Need some help: "BTRFS critical (device sda): corrupt leaf, slot offset bad: block"

From: Hugo Mills <hugo@carfax.org.uk>
To: Brian B <brian@sd85.net>
Cc: Robert Krig <robert.krig@render-wahnsinn.de>,
	Hans van Kranenburg <hans.van.kranenburg@mendix.com>,
	linux-btrfs@vger.kernel.org
Subject: Re: Need some help: "BTRFS critical (device sda): corrupt leaf, slot offset bad: block"
Date: Tue, 4 Apr 2017 13:48:55 +0000	[thread overview]
Message-ID: <20170404134855.GB11512@carfax.org.uk> (raw)
In-Reply-To: <0eda9836-a4ee-b666-2a05-b4bb26746b1a@sd85.net>

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On Tue, Apr 04, 2017 at 09:29:11AM -0400, Brian B wrote:
> On 04/04/2017 12:02 AM, Robert Krig wrote:
> > My storage array is BTRFS Raid1 with 4x8TB Drives.
> > Wouldn't it be possible to simply disconnect two of those drives, mount
> > with -o degraded and still have access (even if read-only) to all my data?
> Just jumping on this point: my understanding of BTRFS "RAID1" is that
> each file (block?) is randomly assigned to two disks of the array (no

   Arbitrarily assigned, rather than randomly assigned (there is a
deterministic algorithm for it, but it's wise not to rely on the exact
behaviour of that algorithm, because there are a number of factors
that can alter its behaviour).

> matter how many disks are in the array).  So if you remove two disks,
> you will probably have files that were "assigned" to both of those
> disks, and will be missing.
> 
> In short, you can't remove more than one disk of a BTRFS RAID1 and still
> have all of your data.

   Indeed.

   Hugo.

-- 
Hugo Mills             | Some days, it's just not worth gnawing through the
hugo@... carfax.org.uk | straps
http://carfax.org.uk/  |
PGP: E2AB1DE4          |

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