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

[Oliver Fromme]

Alexander Best wrote:
 > On Wed Sep 15 10, Oliver Fromme wrote:
 > > Warren Block <wblock at wonkity.com> wrote:
 > > > [...]
 > > > 8. Alexander Motin has an updated CAM version of the ATA system which 
 > > > will eventually replace the existing one.  In -CURRENT, anyway.  He was 
 > > > kind enough to look at my event handler.  My understanding is that he is 
 > > > looking at implementing the head parking/standby mechanism in that new 
 > > > code.
 > > 
 > > The patch below will work with the new CAM ATA driver
 > > (i.e. ada(4) disks).  It adds a sysctl, so you can switch
 > > the spin-down off if you're going to just reboot:
 > > # sysctl kern.cam.ada.spindown_shutdown=0
 > 
 > i haven't tested your patch yet, but i don't think deciding whether to spin
 > down the hdd should be decided merely from the sysctl value.

It was the most simple and least intrusive way to introduce
some means to switch it on and off.  Of course there might
be better ways to do it.  You're welcome to submit your own
patch.

 > the hdd should spindown when a shutdown has been issued and not spindown,
 > if a reboot has been issued.

Right.  That's why my shutdown wrapper script sets the sysctl
to 0 when the -r option is present (I've got that wrapper
script for ages, for different reasons).

Also, there are cases where it is completely impossible to
decide automatically whether the disks should be spun down
or not.  For example, if the admin issues a shutdown -h
(halt), there's no way for the OS to know in advance whether
the admin is going to switch the machine off or reboot to
multi-user.  So there must be a way for the user to forcibly
enable/disable the spindown feature.  I think a sysctl is
the most appropriate way to do that, isn't it?

Actually, my plan is to have a mask of two bits for the
sysctl (the default value would be 3):

 - bit 0: enable (1) or disable (0) spindown
 - bit 1: automatic (1) or manual (0) setting

With the default setting (i.e. bit 1 == 1), at shutdown time
some facility would look at the reboot(2) "howto" flags and
then set bit 0 to either 0 or 1.

There are several ways where to handle that.  For example,
init(8) could be modified to pass the "howto" value to
rc.shutdown (which could be useful for other purposes, too).
Then a standard rc.d script could handle the spindown sysctl.
The advantage of that solution would be maximum flexibility,
because the actual logic is implemented in an rc.d script.

 > deciding whether freebsd reboots or shuts down cannot be done from a script,
 > since users might use the reboot or halt commands in which case (if i'm not
 > mistaken) all shutdown scripts get skipped.

Right, which is why it is a rather bad idea to use halt(8)
or reboot(8), except in an emergency.  Actually I think the
manpages and handbook should strongly discourage it, and
recommend to use shutdown(8) or init(8) instead, both of
which send a signal to PID 1 by default, so rc.shutdown is
executed properly.

Best regards
   Oliver

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