Tejun Heo wrote:
> sd doesn't stop (unload head) on shutdown. This behavior is necessary
> for multi initiator cases. Unloading head by powering off stresses
> the drive and sometimes produces distinct clunking noise which
> apparently disturbs users considering multiple reports on different
> distributions. halt(8) usually puts the drives to sleep prior to
> shutdown but the implementation is fragile and it doesn't work with
> sleep-to-disk.
>
> This patch implements sd attribute stop_on_shutdown. If set to 1, sd
> stops the drive on non-restarting shutdown. stop_on_shutdown is
> initialized from sd parameter stop_on_shutdown_default which defaults
> to 0. So, this patch does not change the default behavior.
Tejun,
The IMMED bit in the START STOP UNIT cdb is not being set
when your patch stops a drive:
Advantage:
- the power won't be dropped immediately after sending
the command to the drive (assuming the drive gets
its power from the same power supply that shutdown
turns off)
Disadvantage:
- it will delay shutdown proportional to the number of
drives with the stop_on_shutdown attribute set. Say
5 seconds per disk.
Disadvantage (with or without IMMED bit set):
- if another initiator (e.g. on another machine) was
using a different partition on that disk, then it might
get upset (especially if it was running Linux).
[I'm not sure why you say this patch is necessary
in this case.]
BTW SCSI disks typically have a lower start-stop lifetime
rating than ATA disks. This reflects that SCSI disks are
designed to be on 168 hours per week.
Doug Gilbert
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