Linux I/O Questions.

Discussion in 'OT Technology' started by RaginBajin, Dec 23, 2004.

  1. RaginBajin

    RaginBajin Have you punched a donkey today?

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    I have a Dell Poweredge 2650 with a PERC Raid device. The size is approx. 500gb. We run NFS to other machines, while also running a mysql server that is in use quite a bit.

    I have been doing some investigating about mysql to see why we are having some slowness. People suggest to look to see if the I/O is the bottleneck, but I'm really unsure on how to tell. I haven't seen anything really on the web to tell me much.

    I run the hdparm three time to see what the average is and this is the response:

    [[email protected] scsi]# hdparm -t /dev/sda

    /dev/sda:
    Timing buffered disk reads: 82 MB in 3.16 seconds = 25.92 MB/sec
    [[email protected] scsi]# hdparm -t /dev/sda

    /dev/sda:
    Timing buffered disk reads: 48 MB in 3.03 seconds = 15.82 MB/sec
    [[email protected] scsi]# hdparm -t /dev/sda

    /dev/sda:
    Timing buffered disk reads: 88 MB in 3.29 seconds = 26.71 MB/sec


    To me it seems like I do, but I really don't know too much on how to address it. Anyone?
     
  2. crontab

    crontab (uid = 0)

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    "hdparm is crap is meant for IDE devices", per our RedHat TAM. If it's simply ext3, just use dd if=/dev/zero of=output.file count=2000000 bs=1024 and iostat that.

    What type of raid is your volume? Is it one big lun? With our experience, we get better performance from a volumes with multiple lunx that a one lun volume. You can use LVM and create a stripped volume, but growing that particular volume under LVM with ext3 will be a pain.

    And lastly are your duplexes uniform?
     
  3. RaginBajin

    RaginBajin Have you punched a donkey today?

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    It's a Raid 5 setup, and everything is kept in one big lun.

    I don't know how to check duplexes or anything like that. This is my first time really working with Raid setup on the System Admin side. Been doing a lot of development and now we need someone to look at this stuff.
     
  4. crontab

    crontab (uid = 0)

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    Well, you will see a performance hit if there's a lot of I/O saturating your queue depths and if the file system is past ~80%.

    I meant duplexes of the NIC's, switches... Make sure they are all the same. One NIC port that is isn't the same as the rest becomes the weakest link. Do a check check to see if there are any error from ifconfig, if there are none, your network config should be okay.
     

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