Re: Bad RAID1 read performance - Mailing list pgsql-performance
From | Dimitri |
---|---|
Subject | Re: Bad RAID1 read performance |
Date | |
Msg-id | 5482c80a0705301119x5543a151q44b029a9743c933e@mail.gmail.com Whole thread Raw |
In response to | Re: Bad RAID1 read performance (Albert Cervera Areny <albert@sedifa.com>) |
List | pgsql-performance |
As there is no 'continuous space' option on ext3/ext2 (or probably "-f fragment_size" may do a trick?) - I think after some filesystem activity you simply loose continuous space allocation and rather expected sequential reading may be transformed into random seeking of 'logically' sequentual blocks... Rgds, -Dimitri On 5/30/07, Albert Cervera Areny <albert@sedifa.com> wrote: > Hardware isn't very good I believe, and it's about 2-3 years old, but the > RAID > is Linux software, and though not very good the difference between reading > and writing should probably be greater... (?) > > Would you set 512Kb readahead on both drives and RAID? I tried various > configurations and none seemed to make a big difference. It seemed correct > to > 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 > optimal > > for RAID1 on some RAID controllers. > > > > - Luke > > > > On 5/30/07 2:35 AM, "Albert Cervera Areny" <albert@sedifa.com> 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=/dev/zero of=bigfile bs=8k > count=786432 > > > && 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 > > -- > Albert Cervera Areny > Dept. Informàtica Sedifa, S.L. > > Av. Can Bordoll, 149 > 08202 - Sabadell (Barcelona) > Tel. 93 715 51 11 > Fax. 93 715 51 12 > > ==================================================================== > ........................ AVISO LEGAL ............................ > La presente comunicación 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 > ningún fin. Su contenido puede tener información confidencial o > protegida legalmente y únicamente expresa la opinión del > remitente. El uso del correo electrónico vía Internet no > permite asegurar ni la confidencialidad de los mensajes > ni su correcta recepción. En el caso de que el > destinatario no consintiera la utilización del correo electrónico, > deberá ponerlo en nuestro conocimiento inmediatamente. > ==================================================================== > ........................... 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. > ==================================================================== > > > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@postgresql.org so that your > message can get through to the mailing list cleanly >
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