Re: [gentoo-user] How can I power disk off?

[Paul Hartman <paul.hartman+gentoo@gmail.com>]

On Thu, Oct 6, 2011 at 3:21 PM, Mark Knecht <markknecht@gmail.com> wrote:
> On Thu, Oct 6, 2011 at 1:03 PM, Paul Hartman
> <paul.hartman+gentoo@gmail.com> wrote:
>> On Thu, Oct 6, 2011 at 2:44 PM, Mark Knecht <markknecht@gmail.com> wrote:
>>> Paul,
>>>   Would hdparm be advisable if the drive was part of a RAID? I suspect not.
>>>
>>>   I don't think this applies to the OP but for the sake of discussion
>>> why not include RAID as part of the solution, if possible.
>>
>> I use hdparm to set power-saving on all members of my RAID5 and it
>> works (in my case, I'm setting them to never spin-down). I created a
>> file /etc/local.d/hd-power-level-fix.start containing one line:
>>
>> hdparm -B 254 /dev/sd[abcdef]
>>
>> which automatically sets those drives to never spin down.
>>
>> In my original recommendation, I hadn't considered hdparm's "spindown
>> immediately" option. I was thinking of the -B command like I used
>> above, to adjust the "spin down after X idle time" option. If all
>> members of the RAID have the same idle time they'll probably all spin
>> up and down together under normal usage (well, depending what kind of
>> RAID it is, I suppose). In my case, I found the "click, whirr, click,
>> whirr, click, whirr, click, whirr, click, whirr" waiting for 5 disks
>> to spin-up when I accessed the RAID annoying, so I disabled it. (I
>> have not done any power-consumption measurements to see what that's
>> costing me...)
>>
>
> My worry was that if the mdraid daemon saw one drive gone - either
> when starting to spin down or when one spins up slowly - and if mdraid
> didn't understand that all this stuff was taking place intentionally
> then it might mark that drive as having failed.
>
> I can see the utility of spinning down a RAID in something like a home
> video server where I keep movies. The machine could be on, ready to
> serve a movie, but the drives aren't drawing much power.
>
> I suspect that there's a pretty substantial power savings on a big
> RAID if done right, but I haven't done any measurements either.

The drive's not gone, it's not offline, it's just not spinning. I
don't think mdraid would even know that.