Re: mysterious disk access every 5 or 10 seconds

[Erik Walthinsen <omega cse ogi edu>]

On Tue, 9 May 2000, Yung-Hsiang Lu wrote:

> disk LED flashes every 5 or 10 (not 5 to 10, it is

That would be the update daemon.  `cat /proc/sys/vm/bdflush` shows:

40	500	64	256	500	3000	500	1884	2

That last 500 is the number of ticks between superblock flushes.  On an
x86 machine, that's your 5 seconds (HZ is 100).  IIRC this causes a write
to disk every time, not just if something on the filesystem changes, but I
might be wrong.  You can raise this value, but beware that it the higher
you set it, the more state can accumulate in memory without writing it to
disk, therefore and ill-timed crash leaves your disk in a worse state than
usual.

For suggestions on reducing this behavior, look up various HOWTOs on
laptops, where such disk activity, in certain cases, is just plain
dangerous.  If you have a specific application where the disk is supposed
to *stay* spun down, say a car MP3 player, having kupdate regularly
spinning it up just to mess with a few atime's or somesuch can cause, if
not a vehicular crash, at least a head crash.  Bleagh. 

Hope that answers your question sufficiently.

TTYL,
    Omega

         Erik Walthinsen <omega@cse.ogi.edu> - Staff Programmer @ OGI
        Quasar project - http://www.cse.ogi.edu/DISC/projects/quasar/
   Video4Linux Two drivers and stuff - http://www.cse.ogi.edu/~omega/v4l2/
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