spinning down external disk

[Jorge Almeida]

How do you do it?

I have external disks used to backups. They are turned on only for the
needed time, usually, so power consumption and noise are not the
issue. The problem is whether turning off the power switch is bad for
the hardware. I can spin down one of the disks through software
(unbinding the device from the controlling driver, the enclosure has
USB conection). This amounts to desconnecting the usb cable manually.
Other disk will just keep happilly spinning... I suppose it depends on
the enclosure.

Question is: turning off the power will have the same effect as using
sofware, or is it more aggressive?

And anyone knows other approaches?

THX

Jorge Almeida