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    SubjectRe: faster boots?
    Pavel Machek wrote:
    > > > > I've had no luck at all with noflushd on my Toshiba Satellite 4070CDT.
    > > > > It would spin down every few minutes, and then spin up _immediately_,
    > > > > every time. I have no idea why.
    > > >
    > > > Were you using the console? Any activity on ttys causes device inode
    > > > atime/mtime updates which trigger disk spin ups. The easiest way to
    > > > work around this is to run X while using devpts for the ptys.
    > >
    > > I was using X, nodiratime on all /dev/hda mounts. My friend who has the
    > > small VAIO with a Crusoe chip also reports the same problem: noflushd
    > > doesn't work with 2.4 kernels (versions that we tried), and the problem
    > > is the same: it spins down and then spins up immediately afterward.
    > It works for me, 2.4.18 on HP omnibook xe3.
    > You may want to watch /proc/stats to see if it is read or write
    > activity that wakes disk up.

    It's write activity, due to atime updates. I was using nodiratime, but
    that's not good enough because every time an executable is run a load of
    things are accessed.

    I found it interesting that some write activity happens almost
    immediately after the access -- and noflushd is connected in some way.
    If I do this:

    while :; do cat /proc/stat; sleep 1; done

    Then I see a few writes have occurred at nearly every iteration. I
    think that is due to the atime updates, because using "noatime" there
    are no writes at most iterations.

    But more interesting: I only see those few-per-second atime writes while
    noflushd is running. If I kill noflushd then they go away.

    So, noflushd triggers some kind of regular write activity. Either
    killing noflushd, or mounting with "noatime", makes it go away.

    I don't like "noatime" because some programs monitor
    /var/spool/mail/jamie's atime to decide if there is any new mail. But I
    am using it now anyway.

    With "noatime", I find the disk is able to spin down for 20 seconds. A
    record :-) But not a very useful one.

    When the disk spins up, I see both read and write activity at the same
    time. Of course I have no idea what files are triggering the spin up.
    (And atime is switched off so I can't use that as a guide!)

    I am a bit surprised that "noatime" makes a difference -- I thought that
    if noflushd spun down a disk, then pending inode writes should be
    delayed until a read or excess memory pressure forces a spin up.

    So: "noatime" is definitely required, to spin the disk down for more
    than an instant. But even that is not good enough. I have 192MB RAM,
    btw. Is that enough to expect longer spin down times than 20s?

    -- Jamie
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