[SATLUG] RAID 5 and 0

Tweeks tweeksjunk2 at theweeks.org
Fri May 16 22:01:52 CDT 2008


On Friday 16 May 2008 08:00:31 pm 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?

No.
If you put four drives in a RAID-0, and the statistical failure rate of each 
of those drives is one failure in four years of its on line date, then four 
of those drives in a RAID-0 will have a statistical life span is 1/4 of that 
(or one year).  So in one year (avg) your system will go down and you will 
lose all of your data. Even a hot spare can't save you.  Backups will save 
most of your data, but not your uptime.

If you want the speed of RAID-0 but the reliability of RAID-5, then you're 
looking for RAID-10 (a bunch of RAID-1 mirrors striped into a big RAID-0).  
This will get you the best of both worlds.. (speed and high availability)  
The down site is the cost.  Basically, you only get the 1/2 the space all of 
the raw drives (i.e. 4 1TB drives in a RAID-10 yield only 2TB). 

Oh.. while you're at it.. if it's speed you're after, you'll also want your 
RAID card to feature battery backed up cache RAM and write through cache 
config in the card config.  LSI and Vortex cards are pretty nice. 

Tweeks


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