[SATLUG] RAID 5 and 0

Brad Knowles brad at shub-internet.org
Fri May 16 22:16:51 CDT 2008

On 5/16/08, Chris Lemire wrote:

>  Instead of using RAID 5, I thought of a different plan. I went online and
>  saw that RAID 5 speed still does not compare to RAID 0. I decided that I
>  could put everything in RAID 0 except one extra drive used for backups.
>  Cron can make nightly backups of only files worth keeping to that extra
>  drive. Is this a good idea?

RAID-0 is great for speed, but the reliability of the RAID array goes 
down very, very rapidly as you increase the size of the array. 
Whereas you might have previously had two drives, each with an MTBF 
of 100,000 hours, now you might have a combined MTBF of only 10,000 
hours.  And when one of those drives fail, the whole RAID array will 
be down and you'll have to spend time rebuilding and restoring from 
backup, which could take quite some time.

And the backups are point-in-time -- nothing written to the array 
after the last backup is going to be saved.  In addition, you're 
probably not going to test the backups until there is a failure, at 
which point would be a horrible time to find out that none of the 
backups have ever worked.  If you're going to be doing backups, you 
need to be regularly testing them to make sure they worked.

But if you can live with these issues, then I see no reason why you 
can't try RAID-0 instead of RAID-5.

But to be honest, if it was my machine, I think I might do RAID-0 
just for the part of the filesystem that needs the higher-speed 
performance, and put everything else on more reliable storage, even 
if that is slower -- and even if it was just a single disk.

Brad Knowles <brad at shub-internet.org>
LinkedIn Profile: <http://tinyurl.com/y8kpxu>

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