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Date: Tue, 30 Dec 2014 21:45:16 -0500
From: Phillip Susi <psusi@ubuntu.com>
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To: ashford@whisperpc.com,
        Jose Manuel Perez Bethencourt <jmperezbeth@gmail.com>
CC: Chris Murphy <lists@colorremedies.com>, "sys.syphus" <syssyphus@gmail.com>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: I need to P. are we almost there yet?
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On 12/30/2014 06:17 PM, ashford@whisperpc.com wrote:
> I believe that someone who understands the code in depth (and that
> may also be one of the people above) determine exactly how BTRFS
> implements RAID-10.

I am such a person.  I had a similar question a year or two ago (
specifically about raid10  ) so I both experimented and read the code
myself to find out.  I was disappointed to find that it won't do
raid10 on 3 disks since the chunk metadata describes raid10 as a
stripe layered on top of a mirror.

Jose's point was also a good one though; one chunk may decide to
mirror disks A and B, so a failure of A and C it could recover from,
but a different chunk could choose to mirror on disks A and C, so that
chunk would be lost if A and C fail.  It would probably be nice if the
chunk allocator tried to be more deterministic about that.


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