From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hugo Mills Subject: Re: Balance RAID10 with odd device count Date: Tue, 21 Feb 2012 01:21:48 +0000 Message-ID: <20120221012148.GD5350@carfax.org.uk> References: <20120221010724.GB5350@carfax.org.uk> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="VMt1DrMGOVs3KQwf" Cc: Wes , linux-btrfs@vger.kernel.org To: tom@drdabbles.us Return-path: In-Reply-To: List-ID: --VMt1DrMGOVs3KQwf Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Feb 20, 2012 at 08:13:43PM -0500, Tom Cameron wrote: > On Mon, Feb 20, 2012 at 8:07 PM, Hugo Mills wrote: > > > > =A0 However, you can remove any one drive, and your data is fine, which > > is what btrfs's RAID-1 guarantee is. I understand that there will be > > additional features coming along Real Soon Now (possibly at the same > > time that RAID-5 and -6 are integrated) which will allow the selection > > of larger numbers of copies. > > >=20 > Is there a projected timeframe for RAID5/6? I understand it's > currently not the development focus of the BTRFS team, and most > organizations want performance over capacity making RAID10 the clear > choice. But, there are still some situations where RAID6 is better > suited (large pools of archive storage). Rumour has it that it's the next major thing after btrfsck is out of the door. I don't know how accurate that is. I'm just some bloke on the Internet. :) > Also, do we know if the RAID5/6 implementation will simply break data > into two data objects and one or two parity objects, or will it work > with an arbitrary number of devices? Meaning, if I have a RAID6 pool > of 12 drives, will I get 10 data objects and two parity objects? AFAIK, the original implementation looked something like the RAID-0 code, so if you have n drives with space for the next block group, it'll take all n drives to use for the block group. Parity is then allocated out of those n (with the distribution of the parity blocks across different drives, as RAID-5 and -6 should do). So, allocating a RAID-6 block group of width 1G on your example 12-drive machine, you will indeed end up with 10G of space in that block group, and 2G of parity data spread across all 12 drives. I don't know if the code that will be delivered will allow you to set a smaller fixed-size stripe width (e.g. 4 data + 2 parity over 8 drives). If the 3-copies RAID-1 code rumour is also true, I would hope so. Again, I'm just some bloke on the Internet... Hugo. --=20 =3D=3D=3D Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk= =3D=3D=3D PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- I'd make a joke about UDP, but I don't know if --- =20 anyone's actually listening... =20 --VMt1DrMGOVs3KQwf Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iD8DBQFPQvGsIKyzvlFcI40RAjPCAKCiDTvatL+OwNmhkAQJILu0AatYygCghpqr eYRXm7QLDhJ/g0ULe/qLjhA= =3E23 -----END PGP SIGNATURE----- --VMt1DrMGOVs3KQwf--