Summary: Re: Spin down HDD after disk sync or before power off

[Alexander Best]

On Thu Oct 21 10, Dag-Erling Smørgrav wrote:
> Alexander Best <arundel at freebsd.org> writes:
> > since there seems no way to distinguish between these two states in ATA(4) it's
> > probably better to leave it as it is, since doing spin downs upon reboot might
> > be even worse than not doing spindowns upon shutdown.
> 
> No.  Where did you get that idea?  To repeat what I've said before -
> several times - in this thread, a modern disk drive can handle hundreds
> of thousands of controlled unloads but only a few hundred emergency
> unloads. Given the choice between "never spin down" and "always spin
> down", the safe alternative is "always spin down".

atacontrol(8) says that:

    "You should not set a spindown timeout on a disk with / or syslog logging
     on it as the disk will be worn out spinning down and up all the time."

this seems to indicate that spinning down a disk has quite an impact.

while chatting with bruce cran regarding this matter we discovered that mav@
already implemented this feature back in february, but disabled it by default
due to issues with the aac controller.

the current implementation (kern.cam.power_down) uses a singe "sleep"
operation, whereas the patch by oliver uses "flush" and "standby immediate".

unfortunately almost nobody was aware of mav's work at the time of the
discussion. would have been nice to have a note in cam(4) explaining the
purpose of kern.cam.power_down. that way a lot of double work could have been
avoided.

is the ATA(4) subsystem still being actively worked on or will it die out after
officially switching to ATA_CAM? the question is, if it is worth implementing
hdd spin down for ATA(4)?

cheers.
alex

> 
> DES
> -- 
> Dag-Erling Smørgrav - des at des.no

-- 
a13x