Received: from localhost (maia-4.hub.org [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id 405729FBDA1 for ; Wed, 30 May 2007 12:00:37 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 48037-05 for ; Wed, 30 May 2007 12:00:33 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.5 Received: from correo10.acens.net (correo10.acens.net [217.116.0.37]) by postgresql.org (Postfix) with ESMTP id 5ACF89FBDF9 for ; Wed, 30 May 2007 12:00:31 -0300 (ADT) Received: (qmail 2840 invoked from network); 30 May 2007 15:00:30 -0000 Received: from unknown (HELO sardina) ([83.175.220.10]) (envelope-sender ) by correo10.acens.net (qmail-ldap-1.03) with SMTP for ; 30 May 2007 15:00:29 -0000 From: Albert Cervera Areny Organization: Sedifa, S.L. To: pgsql-performance@postgresql.org Subject: Re: Bad RAID1 read performance Date: Wed, 30 May 2007 17:00:26 +0200 User-Agent: KMail/1.9.5 Cc: "Luke Lonergan" References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200705301700.26704.albert@sedifa.com> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0.041 tagged_above=0 required=5 tests=AWL=0.040, BAYES_50=0.001 X-Spam-Level: X-Archive-Number: 200705/614 X-Sequence-Number: 25004 Hardware isn't very good I believe, and it's about 2-3 years old, but the R= AID=20 is Linux software, and though not very good the difference between reading= =20 and writing should probably be greater... (?) Would you set 512Kb readahead on both drives and RAID? I tried various=20 configurations and none seemed to make a big difference. It seemed correct = to=20 me to set 512kb per drive and 1024kb for md0. A Dimecres 30 Maig 2007 16:09, Luke Lonergan va escriure: > This sounds like a bad RAID controller - are you using a built-in hardware > RAID? If so, you will likely want to use Linux software RAID instead. > > Also - you might want to try a 512KB readahead - I've found that is optim= al > for RAID1 on some RAID controllers. > > - Luke > > On 5/30/07 2:35 AM, "Albert Cervera Areny" wrote: > > Hi, > > after doing the "dd" tests for a server we have at work I obtained: > > Read: 47.20 Mb/s > > Write: 39.82 Mb/s > > Some days ago read performance was around 20Mb/s due to no readahead in > > md0 so I modified it using hdparm. However, it seems to me that being it > > a RAID1 read speed could be much better. These are SATA disks with 3Gb = of > > RAM so I did 'time bash -c "dd if=3D/dev/zero of=3Dbigfile bs=3D8k coun= t=3D786432 > > && sync"'. File system is ext3 (if read many times in the list that XFS > > is faster), but I don't want to change the file system right now. > > Modifing the readahead from the current 1024k to 2048k doesn't make any > > difference. Are there any other tweaks I can make? > > > > > > ---------------------------(end of broadcast)--------------------------- > > TIP 4: Have you searched our list archives? > > > > http://archives.postgresql.org > > ---------------------------(end of broadcast)--------------------------- > TIP 6: explain analyze is your friend =2D-=20 Albert Cervera Areny Dept. Inform=E0tica Sedifa, S.L. Av. Can Bordoll, 149 08202 - Sabadell (Barcelona) Tel. 93 715 51 11 =46ax. 93 715 51 12 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =2E....................... AVISO LEGAL ............................ La presente comunicaci=F3n y sus anexos tiene como destinatario la persona a la que va dirigida, por lo que si usted lo recibe por error debe notificarlo al remitente y eliminarlo de su sistema, no pudiendo utilizarlo, total o parcialmente, para ning=FAn fin. Su contenido puede tener informaci=F3n confidencial o protegida legalmente y =FAnicamente expresa la opini=F3n del remitente. El uso del correo electr=F3nico v=EDa Internet no permite asegurar ni la confidencialidad de los mensajes ni su correcta recepci=F3n. En el caso de que el destinatario no consintiera la utilizaci=F3n del correo electr=F3nico, deber=E1 ponerlo en nuestro conocimiento inmediatamente. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =2E.......................... DISCLAIMER ............................. This message and its attachments are intended exclusively for the named addressee. If you receive this message in error, please immediately delete it from your system and notify the sender. You may not use this message or any part of it for any purpose. The message may contain information that is confidential or protected by law, and any opinions expressed are those of the individual sender. Internet e-mail guarantees neither the confidentiality nor the proper receipt of the message sent. If the addressee of this message does not consent to the use of internet e-mail, please inform us inmmediately. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20