Spin down HDD after disk sync or before power off

[Tijl Coosemans]

On Thursday 05 March 2009 20:03:45 Tobias Blersch wrote:
> 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.

Quoting that document:

10.4.1 Emergency unload

(...)

Emergency unload is intended to be invoked in rare situations. Because
this operation is inherently uncontrolled, it is more mechanically
stressful than a normal unload.

A single emergency unload operation is more stressful than 100 normal
unloads. Use of emergency unload reduces the start/stop life of the HDD
at a rate at least 100X faster than that of normal unload, and may
damage the HDD.

10.4.2 Required power-off sequence

(...)

You may then turn off the HDD in the following order:
  • Issue Standby Immediate or sleep command.
  • Wait until COMMAND COMPLETE STATUS is returned. (It may take up to
    350ms in typical case).
  • Terminate power to HDD.
This power-down sequence should be followed for entry into any system
power-down state, or system suspend state, or system hibernation state.
In a robustly designed system, emergency unload is limited to rare
scenarios such as battery removal during operation.