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Thread: High iowait

  1. #1

    High iowait

    Hi,

    I am experiencing a high iowait when running the find command as shown below.

    [[email protected] root]# time find / -name "82827635453434243" -print

    real 0m12.430s
    user 0m0.180s
    sys 0m0.420s
    [[email protected] root]#


    ==TOP==

    23:11:33 up 22:23, 3 users, load average: 0.01, 0.05, 0.09
    134 processes: 133 sleeping, 1 running, 0 zombie, 0 stopped
    CPU states: cpu user nice system irq softirq iowait idle
    total 0.0% 0.0% 0.9% 0.0% 0.0% 99.0% 0.0%
    cpu00 0.0% 0.0% 1.4% 0.0% 0.0% 98.5% 0.0%
    cpu01 0.0% 0.0% 0.4% 0.0% 0.0% 99.5% 0.0%
    Mem: 1017328k av, 534404k used, 482924k free, 0k shrd, 120648k buff
    334980k actv, 98876k in_d, 368k in_c
    Swap: 1052248k av, 0k used, 1052248k free 182452k cached

    PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME CPU COMMAND
    10 root 15 0 0 0 0 SW 0.2 0.0 0:01 0 kupdated
    15 root 15 0 0 0 0 DW 0.2 0.0 0:07 1 kjournald
    19938 root 15 0 1080 1080 804 R 0.2 0.1 0:05 0 top
    20116 root 18 0 512 512 344 D 0.2 0.0 0:00 0 find
    1 root 15 0 512 512 452 S 0.0 0.0 0:05 0 init
    2 root RT 0 0 0 0 SW 0.0 0.0 0:00 0 migration/0
    3 root RT 0 0 0 0 SW 0.0 0.0 0:00 1 migration/1
    4 root 15 0 0 0 0 SW 0.0 0.0 0:00 1 keventd
    5 root 34 19 0 0 0 SWN 0.0 0.0 0:00 0 ksoftirqd/0
    6 root 34 19 0 0 0 SWN 0.0 0.0 0:00 1 ksoftirqd/1
    9 root 25 0 0 0 0 SW 0.0 0.0 0:00 1 bdflush
    7 root 15 0 0 0 0 SW 0.0 0.0 0:00 1 kswapd
    8 root 15 0 0 0 0 SW 0.0 0.0 0:12 0 kscand


    This machine is a CentOS 3.3. I have another RedHat 9 server but the same find command shows 0% iowait. Instead, RedHat shows around 50% system.

    Would anyone know whether there might be a problem with CentOS?


    Thanks in advance and regards,

    Peter

  2. #2
    It seems weird you have a high io wait with nothing significant running, is there any 'big' disk writing going on ?

  3. #3
    No, but only thing it does is reading entire disk as per the nature of the find command.

  4. #4
    Is the server new, if not you may want to check for a faulty HD.
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  5. #5
    The server is new.
    I don't thing it's a faulty disk since there are two disks which do the same thing.
    Would this be normal for CentOS? I've never had this problem with RedHat 9 servers.

  6. #6
    Join Date
    Nov 2002
    Posts
    510
    This is normal on CentOs 3.4 ( I think 3.3 as well ) servers. Find command always increases the IOWAIT and it can go upto 100%. RedHat 9 doesn't supports IOWAIT by default, you need to upgrade kernel (If I am not mistaken).
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