[RndTbl] Hard drives

Dan Keizer dan at keizer.ca
Mon Jan 14 11:11:45 CST 2013

Some further comments on Sean's excellent notes:

On 13-01-14 02:22 AM, Sean Cody wrote:
> I'd also recommend avoiding as much RAID as possible that's not controller independent mirroring.
> That is 2x3TB in RAID-1 is the best option where reliability is the biggest concern and a third 3TB drive to do periodic offline backup (ie. store it in a box somewhere and not plugged in).
I've always preferred hardware RAID over software - mostly from a
historical background, reliability etc.
> RAID-10 is better than RAID-5 only because it reduces the width of the stripe but you still have to build a full mirror on failure so it's only marginally better than RAID-5 (unless you can take the two known good halves and use a software RAID-1 in read-only to recover but still not a good plan.
The largest value of RAID10 over RAID5 from an applications standpoint
comes from performance.  For any application (primarily DB systems) with
a large number of random updates, RAID5 can bring your application to a
crawl.  Trying to perform table or batch updates can really suck on
RAID5.  It's not just the time for tables with millions of records, but
when you're processing on a time-line, those extra few minutes per
update add-up.  (How much is everyone's time worth).
> Simply put the more drives in the array the higher the probability of failure relative to MBTF.  If storage greater than the largest available disk is needed my suggestion is either to go RAID-6 or minimal RAID-10 with both a cold and hot spare.
> To cap off this rather long rant of trivia… remember RAID is not in any sense of the imagination a backup.
Agreed - RAID is no panacea.  Guarantee your survival with proper backup
strategies - at some point, hardware will fail - and it's up to us to
bring things back to normal.  With increased striping comes increased
performance - you get what you pay for.  Don't just take RAID5 because
it's cheaper and someone says it will perform "just fine" - look at the
applications that are hosted on the machine and the impact it will have
- and weigh the consequences for your environment.


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