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
