Spin down HDD after disk sync or before power off

[Oliver Fromme]

Alexander Best <alexbestms at wwu.de> wrote:
 > because of kern/140752 i looked through a discussion back in 2009
 > (http://lists.freebsd.org/pipermail/freebsd-hackers/2009-March/027879.html)
 > concerning freebsd's hdd spin down procedure. right now ATA_FLUSHCACHE is
 > being used although the hitachi hdd specs referenced in the pr say that this
 > will not cause proper load/unload and thus an emergency unload will occur
 > which reduces the life expectancy of hdds dramatically (20.000 shutdowns vs.
 > 600.000 shutdowns). unfortunately the discussion back then didn't come up with
 > any sort of decision/patch.
 > 
 > attached you'll find a very simple patch which issues ATA_STANDBY_IMMEDIATE
 > instead of ATA_FLUSHCACHE during hdd spin down.

A few comments ...

First, you should not *replace* ATA_FLUSHCACHE.  Rather, you
should issue *both* commands, first ATA_FLUSHCACHE and then
ATA_STANDBY_IMMEDIATE (maybe with a short delay between, just
to be on the safe side).

Second, you should make sure that ATA_STANDBY_IMMEDIATE is
only used when a poweroff is requested, but not in other
cases.  Of course, ATA_FLUSHCACHE should *always* be sent.

Finally, it would be nice if it is put under a sysctl or
similar, so the feature can be switched on and off.

Best regards
   Oliver

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