RAID

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RAID

Harry-657490

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August 18, 2009 at 12:36 am

#209636

Comments posted to this topic are about the item RAID

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Aaron N. Cutshall SSCrazy Eights Points: 8992 More actions · Answer 1

Doh!! Goes to show what you get when you click through something too quickly without checking your answers! (I checked 0 when I meant to check 1).

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marklegosz SSCrazy Points: 2816 More actions · Answer 2

I was shocked to see only 49% getting this right (when I checked). Surely all DBAs should be all over this one.

kramaswamy SSCoach Points: 18181 More actions · Answer 3

another one of those questions straight from my database course 😛

Aaron N. Cutshall SSCrazy Eights Points: 8992 More actions · Answer 4

marklegosz (8/18/2009)
I was shocked to see only 49% getting this right (when I checked). Surely all DBAs should be all over this one.

Yeah, it was a "no-brainer" and evidently my brain didn't click the right one!!

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sknox SSChampion Points: 12388 More actions · Answer 5

marklegosz (8/18/2009)
I was shocked to see only 49% getting this right (when I checked). Surely all DBAs should be all over this one.

My guess is that many made the mistake that I did - I selected the answer that ONLY protects against a single disk failure (i.e, RAID 1). I don't think in terms of multiple answer questions well... :ermm:

marklegosz SSCrazy Points: 2816 More actions · Answer 6

Yeah, I can't really say too much as I've got some no-brainers wrong before too.

skutnar Valued Member Points: 68 More actions · Answer 7

Actually, RAID 5 is the only RAID level that guarantees protection for at most one disk failure. RAID 1 and RAID 10, depending on how they are configured, can protect against more than one. There is no strict definition that says RAID 1 must only be a mirrored *pair*.

Michael Poppers SSCrazy Points: 2149 More actions · Answer 8

Aaron N. Cutshall (8/18/2009)
Doh!! Goes to show what you get when you click through something too quickly without checking your answers! (I checked 0 when I meant to check 1).

Ditto :-).

Jing. SSC Eights! Points: 956 More actions · Answer 9

Jing.

SSC Eights!

Points: 956

October 16, 2009 at 1:16 pm

#1067146

totally agreed with sknox. 🙂

TomThomson SSC Guru Points: 104773 More actions · Answer 10

I knew what the answer would be, so I got it "right". But "right" has to be in quotes, because it is actually wrong for application screnarios where disk utilisation is high - - the fact is that if decent disc performance is required then RAID 5 provides no protection against single disc failure, for two reasons: (i) during disc recovery the RAID's performance will not be adequate to support your workload, and (ii) disc recovery takes far longer than for RAID 10 and any disc failure during that recovery is a catastrophic failure (while for RAID 10 during recovery there is only 1 disc whose failure would be catastrophic). Every DBA who is involved in making storgae decisions should read and fully understand the material at http://www.baarf.com.

Or for a view from a RAID manufacturer who decided that RAID5 was no longer worth supporting see

http://et.aset.psu.edu/working_notes/storage/iSCSI/docs/Intransa_RAID_White_paper.pdf.

That paper from Intransa was 6 years ago! And the way disc drive technology is changing - drive storage capacity going up much faster than disc throughput - the performance and security hits against raid 5 are getting bigger every year while the cost savings of raid 5 against raid 10 are getting less every year.

RAID 5 is OK if your database has a very low write rate and you can accept a disc read throughput reduction by a factor of 4 or more (depending on number of spindles in the set) during disc recovery; it's useless otherwise. It's good for holding read-only tables, provided the read rate is low enough. It's almost always bad news for transaction logs, for tables that are frequently updated, for tables that grow rapidly, and for applications very high disc throughput.

Tom

rtelgenhoff SSC Eights! Points: 928 More actions · Answer 11

http://en.wikipedia.org/wiki/RAID

Raid 1 requires a minimum of 2 disks and protects against n-1 disk failures, not a 'single' disk failure, although it would protect against any 'single' disk failure even in it's minimum configuration. Raid 5 is the only selection available that never protects against more than a 'single' disk failure. More guessing games to try to figure out the author's meaning. Some authors are just being straightforward like this one and some seem to try to trick you with semantics. :w00t: