From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Hill Subject: Re: XFS on top RAID10 with odd drives count and 2 near copies Date: Wed, 15 Feb 2012 08:30:58 +0000 Message-ID: <20120215083058.GA8821@cthulhu.home.robinhill.me.uk> References: <4F35E925.6000003@hardwarefreak.com> <4F38FD5D.1010201@hardwarefreak.com> <20120213230228.GA5822@www5.open-std.org> <4F39D9B2.3050305@hardwarefreak.com> <20120214113832.GA6157@www5.open-std.org> <4F3AEDEF.2000608@hardwarefreak.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="TB36FDmn/VVEgNH/" Return-path: Content-Disposition: inline In-Reply-To: <4F3AEDEF.2000608@hardwarefreak.com> Sender: linux-raid-owner@vger.kernel.org To: Stan Hoeppner Cc: keld@keldix.com, CoolCold , Linux RAID List-Id: linux-raid.ids --TB36FDmn/VVEgNH/ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue Feb 14, 2012 at 05:27:43PM -0600, Stan Hoeppner wrote: > Maybe I simply don't understand this 'magic' of the f2 and far layouts. > If you only read the "faster half" of a spindle, does this mean writes > go to the slower half? If that's the case, how can you read data that's > never been written? >=20 Writes go to both halves, as normal for a mirrored setup, which is why its write performance is lower than that of a near layout array (more head movement required). Reads will (normally) come from the faster (outer) half of the disk though, so read performance is better. In most cases workloads are read-heavy, so this comes out as a significant gain. Cheers, Robin --=20 ___ =20 ( ' } | Robin Hill | / / ) | Little Jim says .... | // !! | "He fallen in de water !!" | --TB36FDmn/VVEgNH/ Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (GNU/Linux) iEYEARECAAYFAk87bUEACgkQShxCyD40xBJzNgCggl/nTPbV/U7WM0HqPA9VM1oT UQkAnjLjC/PcoDw/AaO8fQvaoHXn65ra =Bw05 -----END PGP SIGNATURE----- --TB36FDmn/VVEgNH/--