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

[Mark Knecht]

On Thu, Oct 6, 2011 at 1:28 PM, Michael Mol <mikemol@×××××.com> wrote:
> On Thu, Oct 6, 2011 at 4:21 PM, Mark Knecht <markknecht@×××××.com> wrote:
>> On Thu, Oct 6, 2011 at 1:03 PM, Paul Hartman
>> 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.
>
> Does mdraid even have an awareness of timeouts, or does it leave that
> to lower drivers? I think the latter condition is more likely.
>
> I suspect, though, that if your disk fails to spin up reasonably
> quickly, it's already failed.
>

In general I agree. However drives that are designed for RAID have a
feature known as Time Limited Error Recovery (TLER) which supposedly
guarantees that they'll get the drive back to responding fast enough
to not have it marked as failed in the RAID array:

http://en.wikipedia.org/wiki/Time-Limited_Error_Recovery

When I built my first RAID I bought some WD 1TB green drives, built
the RAID and immediately had drives failing because they didn't have
this sort of feature. I replaced them with RAID Edition drives that
have the TLER feature and have never had a problem since. (Well, I
actually bought all new drives and kept the six 1TB drives which I'd
mostly used up for other things like external eSATA backup drives,
etc...)

Anyway, I'm possibly over sensitized to this sort of timing problem
specifically in a RAID which is why I asked the question of Paul in
the first place.

Cheers,
Mark