Spin down HDD after disk sync or before power off

[Nate Eldredge]

On Thu, 5 Mar 2009, Tobias Blersch wrote:

> Oliver Fromme wrote:
>> > Joerg Sonnenberger wrote:
>> > This is not true. Many hard disks don't like having to do an emergency
>> > shutdown as it affects the disk life time negatively. That's what
>> > happens if you poweroff the machine when the disks are still spinning.
>>
>> Can you point to any authoritative information (URL) about
>> that claim, such as vendor specs, white paper or similar?
>
> http://www.hitachigst.com/tech/techlib.nsf/techdocs/28DCCB17E0EEC5A086256F4E006E2F5B
>
> Thats the specification for my notebooks hard drive. Section 6.6
> Reliability gives data about how to power-off the disk. It also contains
> numbers of supported load/unloads and emergency unloads. Emergency
> unloads are invoked when the heads are still loaded and power fails.

Ok, I didn't know that.  There are some drives that can unload the 
heads normally on power loss and don't need any special handling, and I 
was under the mistaken impression that this was universal.

But the documentation suggests that this should be a BIOS function.  When 
the kernel tries to poweroff the system, isn't that normally done via the 
BIOS (perhaps with ACPI/APM)?  So maybe the BIOS is supposed to unload the 
heads (by sending a standby/sleep command) before cutting the power.

This makes sense in some ways.  Suppose the drive is attached to a weird 
ATA controller that FreeBSD doesn't know anything about.  (Maybe it's used 
by the other system in a dual-boot setup.)  There's no way that FreeBSD 
could send it a power-down sequence, but the BIOS could.

Perhaps the OP's BIOS for some reason doesn't do this correctly.

-- 

Nate Eldredge
neldredge at math.ucsd.edu