From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Tokarev Subject: Re: raid6 + caviar black + mpt2sas horrific performance Date: Thu, 31 Mar 2011 11:11:48 +0400 Message-ID: <4D942934.3030605@msgid.tls.msk.ru> References: <20110330080823.GA9167@apartia.fr> <4D933435.3010709@gmail.com> <20110330152011.GA6863@apartia.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110330152011.GA6863@apartia.fr> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids 30.03.2011 19:20, Louis-David Mitterrand wrote: [] > /dev/mapper/cmd1 / xfs defaults,inode64,delaylog,logbsize=3D262144 0= 0 > /dev/mapper/cmd1 / xfs defaults,inode64,delaylog,logbsize=3D262144 0= 0 >=20 >> [root@vault t]# dd if=3D/dev/zero of=3D/backup/t/big.file bs=3D32k c= ount=3D32000 >=20 > 1048576000 octets (1,0 GB) copi=E9s, 0,870001 s, 1,2 GB/s > 1048576000 bytes (1.0 GB) copied, 9.11934 s, 115 MB/s Are you sure your LVM volumes are aligned to raid stripe size correctly= ? Proper alignment for raid levels with parity is _critical_, and with 8-drive raid6 you'll have 6 data disks in eash stripe, but since LVM can only align volumes to a power of two, you'll have 2 unaligned volumes after each aligned... Verify that the volume starts at the raid stripe boundary, maybe create new volume and recheck -- there should be quite dramatic speed difference like the above when you change from aligned to misaligned. /mjt -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html