SUMMARY: fsflush once again

From: Alan McKay (
Date: Fri Jan 05 1996 - 08:21:28 CST

Here is a final piece of info on fsflush that I think is extremely


 This is from Adrian Cockcroft's Book "Sun Performance and Tuning" from

  autoup and tune_t_fsflushr

    Unlike SunOS 4 when the update process does a full sync of memory to
    disk every 30 seconds, Solaris 2 uses the fsflush daemon to spread
    out the sync workload. Autoup is set to 30 seconds by default, amd
    this is the maximum age of any memory resident filesystem pages that have
    been modified. Unlike update, fsflush wakes up every 5 seconds (set by
    tune_t_fsflushr) and checks a portion of memory on each invocation
    (5/30 = one-sixth of total RAM by default). The pages are queued on the
    same list that the pageout daemon uses and are formed into clustered
    sequential writes.

    On machines with more then a few hundred Mbytes of RAM, fsflush can take
    over almost an entire CPU in the worts case, when very many pages are
    being modified. This problem can be avoided by reducing the rate at which
    fsflush checks memory. It should still always wake up every few seconds,
    but autoup can be increased from 30 seconds to a few hundred seconds if
    required. In most cases, the files that are being written are closed
    before fsflush gets around to them. For NFS servers all writes are
    synchronous so fsflush is hardly needed at all. Note the time and the CPU
    usage of fsflush, then watch it later and see if its CPU usage is more
    then five percent. If it is, increase autoup as showen.

   set autoup=240 (in /etc/system)


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