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Date: Mon, 9 Feb 2015 22:47:40 +0000
From: Hugo Mills <hugo@carfax.org.uk>
To: Rich Freeman <r-btrfs@thefreemanclan.net>
Cc: Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: btrfs raid5 with mixed disks
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On Mon, Feb 09, 2015 at 05:24:42PM -0500, Rich Freeman wrote:
> How does btrfs raid5 handle mixed-size disks?  The docs weren't
> terribly clear on this.
>=20
> Suppose I have 4x3TB and 1x1TB disks.  Using conventional lvm+mdadm in
> raid5 mode I'd expect to be able to fit about 10TB of space on those
> (2TB striped across 4 disks plus 1TB striped across 5 disks after
> partitioning).  How much would btrfs be able to store in the same
> configuration?  I did see something about being able to use fixed-size
> stripes, and I'm not sure if this helps.  If it does, are there any
> penalties, especially with future expansion of the array?
>=20
> With raid1 mode btrfrs is reasonably smart about mixed disk sizes, and
> you usually end up with half of the total space available.

   http://carfax.org.uk/btrfs-usage/ may be useful here.

   Hugo.

--=20
Hugo Mills             | "It was half way to Rivendell when the drugs began
hugo@... carfax.org.uk | to take hold"
http://carfax.org.uk/  |                                      Hunter S Tolk=
ien
PGP: 65E74AC0          |                        Fear and Loathing in Barad =
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