From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: misunderstanding of spare and raid devices? - and one question more Date: Thu, 30 Jun 2011 10:44:38 -0400 Message-ID: <4E0C8BD6.1080907@turmel.org> References: <4E0C5539.4030000@gmx.de> <4E0C5E47.5090604@anonymous.org.uk> <4E0C6CC4.3030506@turmel.org> <4E0C7196.1070307@gmx.de> <4E0C7B4B.7090404@turmel.org> <4E0C8685.3020806@gmx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4E0C8685.3020806@gmx.de> Sender: linux-raid-owner@vger.kernel.org To: =?UTF-8?B?S2Fyc3RlbiBSw7Zta2U=?= Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 06/30/2011 10:21 AM, Karsten R=C3=B6mke wrote: > Hi Phil >> >> If your CPU has free cycles, I suggest you run raid6 instead of raid= 5+spare. >> >> Phil >> > I started the raid 6 array and get: >=20 > Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] > md0 : active raid6 sde5[4] sdd5[3] sdc5[2] sdb2[1] sda3[0] > 13759296 blocks level 6, 64k chunk, algorithm 2 [5/5] [UUUUU] > [=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D>...] resy= nc =3D 87.4% (4013184/4586432) finish=3D0.4min speed=3D20180K/sec >=20 > when I started the raid 5 array I get >=20 > md0 : active raid5 sdd5[4] sde5[5](S) sdc5[2] sdb2[1] sda3[0] > 13759296 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_] > [=3D>...................] recovery =3D 6.2% (286656/4586432) = finish=3D0.9min speed=3D71664K/sec >=20 > so I have to expect a three times less write speed - or is this calcu= lation > to simple ? That's a bigger difference than I would have expected for resync, which= works in full stripes. If you have a workload with many small random = writes, this slowdown is quite possible. Is your CPU maxed out while writing to the raid6? Can you run some speed tests? dd streaming read or write in one window= , with "iostat -xm 1" in another is a decent test of peak performance. = bonnie++, dbench, and iozone are good for more generic workload simula= tion. Phil -- 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