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    SubjectRe: I/O and pdflush
    On Mon, Aug 31, 2009 at 18:57, Daniel J Blueman<daniel.blueman@gmail.com> wrote:
    > On Jul 11, 6:30 pm, Fernando Silveira <fsilve...@gmail.com> wrote:
    >> The problem is that after some time of data writing at 70MB/s, it
    >> eventually falls down to about 25MB/s and does not get up again until
    >> a loooong time has passed (from 1 to 30 minutes). This happens much
    >> more often when "vm.dirty_*" settings are default (30 secs to expire,
    >> 5 secs for writeback, 10% and 40% for background and normal ratio),
    >> and when I set them to 1 second or even 0, the problem happens much
    >> less often and the sticking period of 25MB/s is much lower.
    > [snip]
    >
    > Generally, this sounds symptomatic of the (now well-documented)
    > internal block management of the SSD delaying writes significantly
    > over long use periods - the output from eg 'vmstat 3' will show all
    > the time spent in I/O wait of course.
    >
    > In your case, the OCZ Core v2 SSD uses the famed JMicron JMF602 which
    > chokes up with outstanding write requests, destroying latency and
    > throughput with it. OCZ won't be releasing newer firmware for the Core
    > v2, so one last-ditch option is to install the newer stock (non-OCZ
    > validated, thus invalidating the warranty) JMicron firmware, which
    > alleviates this somewhat. I've found this successful, though it's
    > tricky to find!

    Thanks, I'll keep that in mind. If no other safer solution else helps,
    I'll update the JMicron.

    > One other idea is to ensure the filesystem starts on an (at least)
    > 128KB boundary, so as to submit complete erase blocks (usually 128KB).

    I don't use any kind of filesystem, just plain sequential data dump. I
    can change the block size for each write(2), but I'm already using a
    huge one: 4MB. I tried lower and higher values before but it seems
    that the 70~80MB/s rate is only reached with blocks of 1MB or bigger.

    --
    Fernando Silveira <fsilveira@gmail.com>
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