[SATLUG] OT: RAID setup recommendations

Eli D. Cantu satlug at then7.org
Thu Jan 27 13:14:05 CST 2011


>
> I use RAID5 for my stuff, as the drives I use have a long tail
> (readily available for several years) and the drive sizes/drive counts are
> reasonably small - <1TB & <6 drives.  As the drive count & drive size
> increases the probability for drive failure + Read error during rebuild.
>  In
> cases where the array size is > 6TB there would be a strong consideration
> for RAID6.  The use of hot spare is driven by two things: Availably of
> replacement and time to repair.  If the parts are readily available and you
> don't mind being exposed during the hunt/acquisition of replacement, then
> no
> hot spare is needed.  If parts/time is scarce then hot sparing is advised.
>
> Really it boils down to Capacity/Resources.  If Capacity needs are modest
> and resources are available, then a mirroring RAID is good.  The best
> balance is one of the error correcting RAID levels (3, 5, 6).
>
> Hope that helps!
> John
> --
> _______________________________________________
>
>
...A lot of great info in this thread.  I think linux raid based upon cheap
serial ata drives is an excellent fit for small business and home office.

But as John mentioned, rebuild can be a serious issue, especially with
larger drives and more drives per array. It's important to minimize time for
rebuild (and for more sophisticated configurations, minimize the number of
drives involved in a rebuild). I found in some of my own tests, linux raid
rebuilds seemed very slow.  So I googled and found a nice article, a while
back, that can make a significant difference in rebuild time:

http://www.cyberciti.biz/tips/linux-raid-increase-resync-rebuild-speed.html

The guy reduced rebuild time for an array that used 2TB drives from 22
hours, down to 4 hours!

Doing some rough interpolation, one could guess that using 500Gb drives for
a linux Raid 6, would take about 1 hour to rebuild for a single disk
failure, using the performance increases in the article.

Eli


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