From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen Subject: Re: Performance question, RAID5 Date: Mon, 31 Jan 2011 14:11:31 +0100 Message-ID: <20110131131131.GA26525@www2.open-std.org> References: <20110130094444.68288b0e@natsu> <20110130171533.4c9e236b@natsu> <4D45C3FA.2040900@hardwarefreak.com> <20110131085202.GA25912@www2.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Mathias =?iso-8859-1?Q?Bur=E9n?= Cc: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen , Stan Hoeppner , Roman Mamedov , CoolCold , Linux-RAID List-Id: linux-raid.ids On Mon, Jan 31, 2011 at 09:37:46AM +0000, Mathias Bur=E9n wrote: > On 31 January 2011 08:52, Keld J=F8rn Simonsen wrot= e: > > If your intallation is CPU bound, and you are > > using an Atom N270 processor or the like, well some ideas: > > > > The Atom CPU may have threading, so you could run 2 RAIDs > > which then probably would run in each thread. > > It would cost you 1 more disk if you run 2 RAID5's > > so you get 8 TB payload out of your 12 GB total (6 drives of 2 TB e= ach). > > > > Another way to get better performance could be to use less > > CPU-intensitive RAID types. RAID5 is intensitive as it needs to > > calculate XOR information all the time. Maybe a mirrored > > raid type like RAID10,f2 would give you less CPU usage, > > and the run 2 RAIDS to have it running in both hyperthreads. > > Here you would then only get 6 TB payload of your 12 GB disks, > > but then also probably a faster system. > > > > Best regards > > keld > > >=20 > Hi, >=20 > It's interesting what you say about the XOR calculations. I thought > that it was only calculated on writes? The Atom (330) has HT, so Linu= x > sees 4 logical CPUs. Yes you are right, it only calculates XOR on writes with RAID5.=20 But then I am puzzled what all these CPU cycles are used for. Also many cycles are used on mirrored raid types. Why? Maybe some is because of LVM? I have been puzzled for a long time why ordinary RAID without LVM need to use so much CPU. Maybe a lot of data sguffling between buffers? Neil? Best regards Keld -- 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