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    SubjectRe: Linux 2.6.29
    Linus Torvalds wrote:
    > On Mon, 30 Mar 2009, Ric Wheeler wrote:
    >> A modern S-ATA drive has up to 32MB of write cache. If you lose power or
    >> suffer a sudden reboot (that can reset the bus at least), I am pretty sure
    >> that your above assumption is simply not true.
    > At least traditionally, it's worth to note that 32MB of on-disk cache is
    > not the same as 32MB of kernel write cache.
    > The drive caches tend to be more like track caches - you tend to have a
    > few large cache entries (segments), not something like a sector cache. And
    > I seriously doubt the disk will let you fill them up with writes: it
    > likely has things like the sector remapping tables in those caches too.

    I spent an entire day recently, trying to see if I could significantly fill
    up the 32MB cache on a 750GB Hitach SATA drive here.

    With deliberate/random write patterns, big and small, near and far,
    I could not fill the drive with anything approaching a full second
    of latent write-cache flush time.

    Not even close. Which is a pity, because I really wanted to do some testing
    related to a deep write cache. But it just wouldn't happen.

    I tried this again on a 16MB cache of a Seagate drive, no difference.

    Bummer. :)

     \ /
      Last update: 2009-03-30 18:33    [W:0.021 / U:5.564 seconds]
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