From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jakob Oestergaard Subject: Re: raid 1 vs raid 0+1 Date: Tue, 29 Oct 2002 14:14:53 +0100 Sender: linux-raid-owner@vger.kernel.org Message-ID: <20021029131453.GB24171@unthought.net> References: <200210291229.g9TCTcO05488@gg.cyberlab.de> 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: <200210291229.g9TCTcO05488@gg.cyberlab.de> To: Antonello Piemonte Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Tue, Oct 29, 2002 at 01:29:23PM +0100, Antonello Piemonte wrote: > Hello >=20 > I have a server wich I would like to set up with > mirroring for some data protections (against disk failure). > the machine is supposed to deal mostly with writing of > lots of small files (2kb perhaps 4kb each) to disk (well, array) > and the goal would be to be able to write at least few hundreds=20 > files per seconds (!). >=20 > the question is: for performance, is it better a raid 1 or a=20 > raid 0+1 configuration? is the above load (number of files written > per second) a realistic goal to attain with a SCSI based uniprocessor= PIII=20 > 800MHZ with ext3 file system (this I will tackle separately, perhaps > will use ext2 to increase performance) and 1 Gig of RAM?=20 On a dual PIII-550 with 512 MB of memory, ext3, and a RAID-0+1 (four 40= G 7200rpm IBM IDE Deathstar disks, 64k chunk-size on the RAID-0), I get: $ time for i in {0,1,2,3,4,5,6,7,8,9}; do mkdir $i; for j in {0,1,2,3,4,5,6,7,8,9}{0,1,2,3,4,5,6,7,8,9}; do dd if=3D/dev/zero of=3D$= j/$i bs=3D1k count=3D4; done done real 0m5.024s So, 5 seconds for writing one thousand 4 kb files *sequentially*. Note that I only put 100 files in each directory - if I put 1000 files in one directory, performance would degrade (more significantly when th= e number is, say, 10000). You may want to experiment with ext3 journalling options - you may see better performance on data=3Djournal mode, if you write the files in bursts (with some longer pauses in between). I cannot give you any certain advice here, other than to experiment. RAID-0 will probably allow you to scale better, but I'm really not sure how the performance on this rather perculiar workload changes as you ad= d disks - in any case it will be *highly* filesystem dependent. You should definitely also try out ReiserFS and eventually JFS, XFS, and perhaps even one of the FAT variants (yes, FAT is actually *very* fast for some very particular workloads, because it is so primitive (eg. it gets less in the way) - at least this used to be true, but I do not kno= w if it is still so, and I'm not sure about your workload either). So in short; Everything I said here except for the 5 second benchmark i= s guessing... Now you go measure ;) Please, if you do decide to measure, do post a summary here to the list= =2E I'm sure people will find it interesting, and it will appear in the archives for the next person with the same problem to find. Cheers, --=20 =2E............................................................... : jakob@unthought.net : And I see the elder races, : :.........................: putrid forms of man : : Jakob =D8stergaard : See him rise and claim the earth, : : OZ9ABN : his downfall is at hand. : :.........................:............{Konkhra}...............: - 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