Re: Green drives and RAID arrays with partity

[Joe Landman <landman@scalableinformatics.com>]

On 09/25/2011 07:02 AM, Marcin M. Jessa wrote:
> Hi guys.
>
> I was wondering if it's safe to use so called green drives in RAID 5 or
> RAID 6 with md?

You might need to turn off TLER and their power spin-down features, but 
in general, they *should* work ok.  Modulo any firmware issues (staring 
intently at WD).  We don't use Western Digital drives anymore due to ... 
er ... profound high failure rates we've observed in the field.  These 
may or may not be connected to "greenness".  They are definitely 
connected to buggy firmware (this is on enterprise and consumer drives, 
used across a fairly wide swath of use cases).

Your mileage may vary (e.g. you might have different experiences).  We 
wouldn't recommend them.

> Drive such as Seagate Barracuda® Green 2TB ST2000DL003 or Western
> Digital Caviar® Green™ 2TB WD20EARX have TLER off and reading misc
> forums I understand that it would be a good idea to buy drives with that
> option available.

TLER and the power spindown option are good things to be able to turn 
off.  Otherwise you need to have a way for the MD device to deal with a 
spun-down set of drives.  I am not sure support is there for this right 
now ... I could be wrong, I've just not seen it.

This said, spinning up and down drives is actually more stressful for 
the electronics and motor.  Better to leave them in one state whenever 
possible.  I can't remember the study I saw on this, but about a year 
ago I saw a quietly published correlation between drive failures and 
number of spinup/spindown cycles.  My memory might be off on it, so feel 
free to look for yourself (and don't rely upon my likely faulty memory).

> On the other hand some people claim that Linux/Solaris/BSD based
> software RAID may be able to work just fine with these drives.

If the drives don't try to be "smart" and do "smart things" (powerdown, 
unlimited Herculean error recovery, massive sector remapping that takes 
it out of service for more than 60 seconds), yeah, they should "just 
work".  If you have a barrel full of these drives and need to use them, 
by all means, just turn off the "smart" features.

OTOH, if you are buying new drives, steer clear of them.


-- 
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics, Inc.
email: landman@scalableinformatics.com
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