[gpm] Do I need to spin down my SATA HDD to save power?

[Aaron Whitehouse <lists whitehouse org nz>]

Hello,

I have a new HTPC that is on 24/7 running MythTV, but only used for a
few hours when recording or playing back. It has a relatively modern HDD
in it:
http://www.wdc.com/en/products/products.asp?driveid=307
I think.

I was reading:
http://www.mythtv.co.nz/mythtv/mythtv-articles/power-saving-tips/
and it suggests spinning down HDDs. It also says that, because the HDD
is SATA, this is not easy to do. I then came across this:
http://live.gnome.org/GnomePowerManager/FAQ#head-e6d48e4196eb363908fb71975a5311f11f8dd9e4
which says:
"It's was decided user-configurable powermanagement was not really
required when modern hard disks have really intelligent powermanagment."

The link above (http://www.wdc.com/en/products/products.asp?driveid=307)
suggests that my HDD uses less than 1W on "Standby" or "Sleep", but over
8W for "Idle".

Here's my question - assuming a standard Mythbuntu install with no
changes to hdparm etc., will my HDD move into those "Standby" or "Sleep"
modes automatically, without any intervention from the OS, and reduce
the power consumption to less than 1W? If not, is there some AHCI
command or something that I should be using to make them do so?

Given that it is running constantly, I am also a little concerned about
wear and tear on the disk. Are these (I hope) automatic/low-power states
also low wear and tear, or should I be trying to manually power it down
for this reason?

I posted this here:
https://answers.launchpad.net/ubuntu/+source/gnome-power-manager/+question/73599
but I wasn't completely convinced by the answer.

Thanks in advance for any help!

Aaron