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RAID Recommendations needed for a dedicated SQL server

Posted on 2008-06-12
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Last Modified: 2008-06-25
I am trying to design and implement a server based solution for hosting all our soon to be SQL databases (they are currently MSDE).  I would like to know what the recommended design for the RAID is. I was thinking the following:-
RAID 1 - O/S and programs
RAID 1 - LOG FILES
RAID 5 - Databases
I am torn between RAID 5 or RAID 10 for the databases. I am trying to get the balance between cost v performance v redundancy.
cheers,
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Question by:FBOLTS
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by:slam69
ID: 21769764
Hi,

raid10, mirrored stripe, would be the fastest retrival rate, obiously th emost expensive due to tehredundancy you need to employ

id advice a 6 drive configuration, 3 drives stripe with a 3 disk mirror
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by:kanalQko
ID: 21769778
my recommendations is tu use raid 1+0 rather than raid 5, raid 1+0 has better performance, but if you don`t want waste cash use raid 5, you will loose only only capacity of one harddrive, raid 5 is cheaper redundant solution, raid 1+0 is more expensive, less of capacity, but much more faster
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by:slam69
ID: 21769795
Only use raid 1 for your log file if it is going to be a low volume transaction log, if its going to be a large transactyion log due to lots of writes, deltes etc id go with 10 again for the log files as well, although necessarily a must, just you can spread the log over 2 smaller drives instead of one large one
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by:superiz
ID: 21770652
The question of RAID 5 vs. Raid 1+0 can only be answered meaningfully if you tell me the hardware you intend to use (server model, raid controller model, and disk drives types/quantities). With the right hardware, you will not be able to measure a significant difference between the two.
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by:FBOLTS
ID: 21792969
hi superiz & the rest of the help,
Well i have a few possible solutions:-
1. buy A brand new Dell PE 2950, 4GB, 2 quad core 3.0 Ghz CPU. RAID - Adaptec 39320a, SAS 15K drives. This server only has at most 8 drive bays so i guess the config would be OS mirror (2 drives) Log mirror (2 drives) DB mirror (4 drives).
2. Buy new server (spec as above) config as OS mirror (2), DB and LOGS RAID 1+0 (6 drives)
3. Buy a smaller server similar to spec  above but use an external Array we already have. a reasonably new storageworks HP MSA30 s-b with 15K SCSI . If we go for this config i guess the RAID would be as follows: mirror os (2 on board drives) mirror logs (2 on board drives) RAID 1+0 on external array (6 drives)

The long and short of it is that i need to try and use existing hardware where applicable but if i have to i can buy new hardware. I should say the databases are not  particulary "production facing" they are AV, Blackberry, Insight but the solution needs to be future proofed incase more business critical dbs come online.

A couple of other questions are:- if we used the external array, would the SCSI interface be a bottle neck that could potentially cause pain?

cheers,
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by:andyalder
ID: 21793015
The MSA30 SB starts to become a bottleneck once you go past about 7 disks in the enclosure, solution to that is the dual-bus option.
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by:slam69
ID: 21793059
Hi,

ok take alook at teh following forum post which has so much goon information which whilst not SQL based specifically does relate to yoru hardware questions and drive uncertainties

http://www.webmasterworld.com/webmaster/3606784.htm

Ill pull out some highpoints for you to help you on your way but id recommend reading the whole thing


My prefereable option to the 3 you have listed would be C as you can shop around and buld your own spec hardware and array, the set up can be exactkly what you wish and you arent bound by dells server limitations. Also id consider hp over dell if you go down option 1 route to make sure you get the best out of the hot swap functionality

teh scsi interface shouldnt provide you with a Bottle neck and would be slightly faster (possibly) than SATA although teh cost implications for SCSI are greater, if your not having a huge amount of write activity, which it doesnt appear you will have, then might be more cost effective to look at SATA as not a great deal of difference between the two now.

the dell 8 drive option sounds limited in scalability and dont foget if you employ raid 1+0 you use approx 75% of your disk space due to mirroring, great if high availability is required and no loss of data bad for cost effectiveness and scalability
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Author Comment

by:FBOLTS
ID: 21793306
andyalder - But if i kept the array to 6 disks (RAID 1+0) that should be fine eh?
Slam69 - thanks for the information. We currently have a corporate agreement with Dell under a lease agreement so any new hardware i buy will be dell. So if it were you with my constrainsts what config would you go for? If i were to go for using the array  what config should i use? should i have the logs and the db both on the external array but in separate RAIDs? RAID 1 (log) RAID 5 maybe (db)

sorry for the abundance of questions it just this is a high profile project i am working on and i would like to ensure i am effective both with cost, scalability and performance.

thanks guys.
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by:andyalder
andyalder earned 20 total points
ID: 21793495
6 is fine, the bus becomes the bottleneck faster with sequential I/O and SQL is random anyway. Your problem is that HP aren't going to support a MSA on a Dell and Dell aren't going to support it either even though it will work.
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slam69 earned 210 total points
ID: 21793538
Hi again,

your idea for the raid 1 log and raid 5 for db does sound like the best compromise for you situation if you are bound by dell, you could go with option 1 as you have stated and use 2 disks for your log file mirrored,  two for your OS, and the 3+ 1 for your striped DB. Make sure you have one minimum back up drive for the array as the 3+1 configuration allows for one failure and it can rebuild itself with a hot swap, but 2 strikes  a,d 2 failed hard drives and your array is shot and expensive to try and rebuild.

only use raid 1 though for the logs if its low volume or if its not low volume you would have to perform more regular backup and truncates of the log files.

My one question mark for option 1 is the scope for scalability say you put 250gb drives in each of teh bays, that gives you 750gb of data storage space, seem slike a lot but can soon go so make sure you pick drives with large capacities to future proof your spec. Only you know the growth of your architecture and db's so will have to make the best choice there
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by:superiz
superiz earned 20 total points
ID: 21797156
I have never tested the Adaptec 39320a controller you mentioned, but I do know that if you get the optional Perc6/i (rebraded LSI OEM model) instead, that you can use almost any disk configuration you wish and you will not be able to measure any meaningful performance difference. If you are stuck with the basic embedded controller, or if the Adaptec you mentioned is not one of their current high-end models, then I strongly suggest that you familiarize youself with the disk partition alignment issues with Windows and how to correct them with the latest versions of diskpart avalable in Vista and Server 2008.

See the document titled: Disk performance may be slower than expected when you use multiple disks in Windows Server 2003, in Windows XP, and in Windows 2000
http://support.microsoft.com/kb/929491
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by:andyalder
ID: 21797330
That's bollocks, the physical disk structure isn't even exposed to the OS any more. you can just as easily slow it down as speeding it up with diskparet.exe.
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by:superiz
ID: 21797664
What is a diskparet? Can I get one as a pet?
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by:andyalder
ID: 21800928
Fred Flintstone's record player stylus :)

And the MS doc isn't actually wrong, it's just that you need to confirm with the manufacturer. Alligning is all very well for the outside tracks but the physical disk geometry isn't exposed so you can still expect extra short seeks when you don't expect them. It's normally masked so much by the write cache that you don't notice it.
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