From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Smith Subject: Re: RAID 5 of RAID 5's? Date: Mon, 13 Jun 2005 10:03:39 +0000 Message-ID: <20050613100339.GO750@strugglers.net> References: <1118187572.15459.96.camel@seki.nac.uci.edu> <42A93D30.6080900@apartia.fr> <1118436219.25226.252.camel@seki.nac.uci.edu> <42AD329B.4080103@apartia.fr> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="kcP3xCD2XyuzODov" Return-path: Content-Disposition: inline In-Reply-To: <42AD329B.4080103@apartia.fr> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids --kcP3xCD2XyuzODov Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jun 13, 2005 at 09:15:39AM +0200, Laurent CARON wrote: > Dan Stromberg a ?crit : > >>>Has anyone constructed a RAID 5 of RAID 5's using mdadm on a linux > >>>system? > >>> > >>>Was it reliable? > >>> > >>>How large was it? > > > RAID 10 is IMHO a bit more efficient. >=20 > Raid 5 means at least 9 disks: > Usable capacity: 4 Disks > Read speed: Good > Write speed: poor With a low number of disks, you would indeed get the same or less capacity with RAID 5 + RAID 5 as compared to RAID 10, but as the number of disks gets higher, doesn't the capacity of RAID 5 on top of RAID 5 (we need a name for this, is RAID 55 technically correct?) get better? For example, 30 disks, organised as 10 3-disk RAID 5s, have 9*2 or 18 disks of capacity, whereas a RAID 10 of same would be 15 disks. The write performance seems bad though, and maybe the rebuild time as well. --kcP3xCD2XyuzODov Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (GNU/Linux) iD8DBQFCrVn7IJm2TL8VSQsRAsKrAJ0WLJq5F672YEk1dxON+3h4iVtuOwCeLJKE Tylqv0xlHvjXmkdO7xi49sU= =2RIp -----END PGP SIGNATURE----- --kcP3xCD2XyuzODov--