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    SubjectRe: xfs: very slow after mount, very slow at umount


    On Thu, 27 Jan 2011, Mark Lord wrote:

    > On 11-01-27 12:30 AM, Stan Hoeppner wrote:
    >> Mark Lord put forth on 1/26/2011 9:49 PM:
    >>
    >>> agcount=7453
    >>
    >> That's probably a bit high Mark, and very possibly the cause of your problems.
    >> :) Unless the disk array backing this filesystem has something like 400-800
    >> striped disk drives. You said it's a single 2TB drive right?
    >>
    >> The default agcount for a single drive filesystem is 4 allocation groups. For
    >> mdraid (of any number of disks/configuration) it's 16 allocation groups.
    >>
    >> Why/how did you end up with 7452 allocation groups? That can definitely cause
    >> some performance issues due to massively excessive head seeking, and possibly
    >> all manner of weirdness.
    >
    > This is great info, exactly the kind of feedback I was hoping for!
    >
    > The filesystem is about a year old now, and I probably used agsize=nnnnn
    > when creating it or something.
    >
    > So if this resulted in what you consider to be many MANY too MANY ags,
    > then I can imagine the first new file write wanting to go out and read
    > in all of the ag data to determine the "best fit" or something.
    > Which might explain some of the delay.
    >
    > Once I get the new 2TB drive, I'll re-run mkfs.xfs and then copy everything
    > over onto a fresh xfs filesystem.
    >
    > Can you recommend a good set of mkfs.xfs parameters to suit the characteristics
    > of this system? Eg. Only a few thousand active inodes, and nearly all files are
    > in the 600MB -> 20GB size range. The usage pattern it must handle is up to
    > six concurrent streaming writes at the same time as up to three streaming reads,
    > with no significant delays permitted on the reads.
    >
    > That's the kind of workload that I find XFS handles nicely,
    > and EXT4 has given me trouble with in the past.
    >
    > Thanks


    Hi Mark,

    I did a load of benchmarks a long time ago testing every mkfs.xfs option
    there was, and I found that most of the time (if not all), the defaults
    were the best.

    Justin.


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