Re: [PLUG] Two-Drive Software Raid 5?

[Randall A Sindlinger <rsindlin+plug@seas.upenn.edu>]

On Fri, Jan 07, 2011 at 09:56:59AM -0500, Claude M. Schrader wrote:
> On 09:37 Tue 04 Jan     , Rich Freeman wrote:
>  
> > 1.  I need 1TB of redundant space now.
> > 2.  I only want to pay for 2 1TB hard drives now.
> > 3.  I want to be able to add 1TB at a later date for the cost of 1 1TB
> > drive, and migrate data online (or at least without access to other
> > storage).
> > 
> > I don't really see any other options.
> 
> someone mentioned in irc that 1TB drives are only $59 at microcenter right
> now. I say just buy 3 or 4 now and get it over with. While a 2 drive raid5
> may be theoretically possible, do you really want to trust your data to
> such a crazy untested setup?
> Claude

$59 dollars - 6 cents/Gig - certainly puts the "i" in raid :-)

I feel like discussion on raid 5 is a bit irrelevant for 1TB disks - raid 6 
should be on the table instead.  As JP mentioned, you're looking at over 
24 hours for a disk to copy data over on raid 1.  With raid 5, you need to 
calculate 1 TB of parity, too.  With a larger disk, you increase the number
of "places" you can get a read/write error, too, so it's easier for a disk
to "fail".  And at $59, I wouldn't expect reliable error-free performance.

If you're actually trying to maintain un-interupted access to your data,
raid 5 is just not sufficient once you hit the range of 1TB spindles, and
it's not worth the extra disk (3 vs 2) over raid1 in terms of reliability, imo.
With raid 1, even if both disks fail, standard disk-recovery tools can pull
off data from the "good" parts.

But if you get to that point, that means you weren't doing backups, which
should really be considered before raid levels.

I really liked JP's point - raid 1 is Good Enough.  If you want "Better",
then you really just should go straight to raid 6.

-Randall
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