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    SubjectRe: Slow disks.
    Hi,

    [ccing linux-ide]

    Please provide the part of kernel log showing initialization of your
    disk controller(s) as well as detection of all the discs.
    Verbose lspci output for the disc controller and $(smartctl -i -A $disk)
    output might be useful as well.

    Did you try the individual discs on a completely different system (e.g.
    plain desktop system) and what revision of SATA are both components
    supporting?

    Bruno


    On Mon, 20 December 2010 Rogier Wolff <R.E.Wolff@BitWizard.nl> wrote:
    > Hi,
    >
    > A friend of mine has a server in a datacenter somewhere. His machine
    > is not working properly: most of his disks take 10-100 times longer
    > to process each IO request than normal.
    >
    > iostat -kx 10 output:
    > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
    > sdd 0.30 0.00 0.40 1.20 2.80 1.10 4.88 0.43 271.50 271.44 43.43
    >
    > shows that in this 10 second period, the disk was busy for 4.3 seconds
    > and serviced 15-16 requests during that time.
    >
    > Normal disks show "svctm" of around 10-20ms.
    >
    > Now you might say: It's his disk that's broken.
    > Well no: I don't believe that all four of his disks are broken.
    > (I just showed you output about one disk, but there are 4 disks in there
    > all behaving similar, but some are worse than others.)
    >
    > Or you might say: It's his controller that's broken. So we thought
    > too. We replaced the onboard sata controller with a 4-port sata
    > card. Now they are running off the external sata card... Slightly
    > better, but not by much.
    >
    > Or you might say: it's hardware. But suppose the disk doesn't properly
    > transfer the data 9 times out of 10, wouldn't the driver tell us
    > SOMETHING in the syslog that things are not fine and dandy? Moreover,
    > In the case above, 12kb were transferred in 4.3 seconds. If CRC errors
    > were happening, the interface would've been able to transfer over
    > 400Mb during that time. So every transfer would need to be retried on
    > average 30000 times... Not realistic. If that were the case, we'd
    > surely hit a maximum retry limit every now and then?
    >
    >
    > These syptoms started when the system was running 2.6.33, but are
    > still present now the system has been upgraded to 2.6.36.
    >
    > Is there anything you can suggest to get to the root of this problem?
    > Could this be a software issue with the driver? Can we enable some
    > driver debugging to find out what is wrong?
    >
    > Any help will be appreciated.
    >
    > Roger.
    >


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