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:
> > Dag-Erling Smørgrav <des at des.no> writes:
> > > 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.
> 
> The problem with setting a short idle timeout is that, on a typical
> laptop or desktop system, you end up spinning the disk down and back up
> several hundred times a day, which increases power consumption, I/O
> latency and wear.
> 
> However, a single emergency unload (what happens when the disk loses
> power without first unloading the head) shortens the disk's life
> expectancy as much as hundreds or thousands of controlled unloads.
> 
> Unless you think our users commonly reboot their computers hundreds or
> thousands of times between each time they cycle the power, the safe
> alternative is to *always* spin down during shutdown.
> 
> I truly hope this is the *last* time I have to repeat this.  It's really
> not that hard to understand.

no need to get upset. you asked where i found the information regarding the
wear impact of spinning down disks and i gave you the answer.

i totally agree with you on this issue. yet again: is it worth changing this
for the ata(4) sub system which will probably become obsolete in one or two
years? the ata(4) subsytem exists since FreeBSD 4.0. why introduce this change
now that it's going to die soon?

also as i pointed out in my earlier post, spinning down disks already caused
problems with the aac controller. since not a lot of testing went into the spin
down code one can expect more controller related issues to arise.

cheers.
alex

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

-- 
a13x