Re: [PERFORM] Bad RAID1 read performance
As you suggested with two threads I get 42.39 Mb/s in one and 40.70 Mb/s in the other one, so that's more than 80Mb/s. That's what I expected with a single thread, so thanks for the information. It seems I will have to buy better hard drives if I want increased performance... A Dimecres 30 Maig 2007 22:13, Luke Lonergan va escriure: Not for one thread/process of I/O. Mirror sets can nearly double the read performance on most RAID adapters or SW RAID when using two or more thread/processes, but a single thread will get one drive worth of performance. You should try running two simultaneous processes during reading and see what you get. ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
[PERFORM] Bad RAID1 read performance
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
Re: [PERFORM] Bad RAID1 read performance
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 [EMAIL PROTECTED] 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
Re: [PERFORM] Bad RAID1 read performance
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 [EMAIL PROTECTED] 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 asegurarni la confidencialidad de los mensajes nisucorrecta recepción. Enel 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 individualsender. 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 internete-mail,pleaseinform usinmmediately. ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [PERFORM] Bad RAID1 read 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 [EMAIL PROTECTED] 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 [EMAIL PROTECTED] 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 asegurarni la confidencialidad de los mensajes nisucorrecta recepción. Enel 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 individualsender. 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 internete-mail,pleaseinform usinmmediately. ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [PERFORM] Bad RAID1 read performance
Albert, On 5/30/07 8:00 AM, Albert Cervera Areny [EMAIL PROTECTED] 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... (?) Not for one thread/process of I/O. Mirror sets can nearly double the read performance on most RAID adapters or SW RAID when using two or more thread/processes, but a single thread will get one drive worth of performance. You should try running two simultaneous processes during reading and see what you get. 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. Shouldn't matter that much, but yes, each drive getting half the readahead is a good strategy. Try 256+256 and 512. The problem you have is likely not related to the readahead though - I suggest you try read/write to a single disk and see what you get. You should get around 60 MB/s if the drive is a modern 7200 RPM SATA disk. If you aren't getting that on a single drive, there's something wrong with the SATA driver or the drive(s). - Luke 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 [EMAIL PROTECTED] 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 ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
