RAID 10

Hi Guys,

I have this question running in the MSSQL area also.

I have a running argument with my boss at the moment regarding what RAID set up should be on our new SQL cluster solution.

The current database has two data files on a single filegroup which are heavy in both reads and writes.

The shared storage allows us to allocate 13 disks to this task.  I have choosen to create two RAID 10 arrays (4 disks each) for the data files and split them between these two and one RAID 1 array for the transaction logs.  The remaining disks are used for the quorum drive and global hot spare.

My boss however is querying my logic and suggests removing the two 4 disk RAID 10 arrays and creating one RAID 10 array with 8 disks and placing all the datafiles on the one virtual disk.

I can see his point, however I would like to get some professional opinions on this.  Basically what is better? 2 (4 x disk RAID 10 array) or 1 (8 x disk RAID 10 array).  If someone can give me a definate answer I will give them all the points from both questions.

Many thanks
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n0ch1psAsked:
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mcp_jonCommented:
You can check this page " http://www.acnc.com/04_01_10.html " and there you'll see the Advantages and Disadvantages of Raid 10.

I Would advise you to keep 2 x 4 Raid 10, because that way you have a two point failure option, I mean, if one Raid 10 goes down, you can hold the lines with the other one.

Keep writing !

Best Regards !
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merowingerCommented:
its fatster with 8 disks

mero
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merowingerCommented:
sorry faster!!!!

- a 2 disk RAID 0 can move 30 megs per second
- a 4 disk RAID 10 can move 50 megs per second
- a 8 disk RAID 10 can move 90 megs per second

mero
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mcp_jonCommented:
Mero, is right ! It´s faster, but you'll have only one breakpoint.

Best Regards!
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n0ch1psAuthor Commented:
I'm not that concerned with redundancy with either setup as RAID 10 redundancy is good and as this is an SQL box if I did go for the 2 x 4 disk raid 10 option and one array failed, sql would break anyway.

merowinger - Where did you obtain these performance figures?



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merowingerCommented:
hi,
from
http://support.novell.com/cgi-bin/search/searchtid.cgi?/10094467.htm

but that arent exatly the same numbers, but sure is, that more disks are faster in raid 10

mero
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rindiCommented:
It is always recommended to have transaction logs on different media than than the data itself is. If possible you should have those drives on another controller as well, but since you aren't concerned with redundancy you might as well go for your Boss' suggestion...
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n0ch1psAuthor Commented:
Rindi - The transaction logs will be placed on a RAID 1 array, as per my initial comments.  Unfortunately adding another controller is not an option, if I could do this I would definately then split the two between the controllers, cheers.

mero - Sorry, don't get the wrong impression, I'm not disagreeing with you that adding more disks to a RAID 10 array will speed things up.  I was just interested to see if there was any further information I could get on benchmarks etc, especialy when using this in conjunction with sql data files because of the way the sql engine will use the data file reads/writes etc.

I will humbly go back to my boss and work out how he'd like to continue with this.  Thanks for everyones comments.

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mcp_jonCommented:
Best Regards !
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merowingerCommented:
you#re welcome
hu!!!
mero
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andyalderCommented:
I would tend to agree with your manager, if there's one big array that's twice as fast as the two smaller arrays then the performance should be identical considering that the big array would have twice as much work to do assuming the databases have identical loads.

If one of the databases isn't very busy and the other one is getting hammered though then the time that the array belonging to the not busy database will be available to the other busy database so the single big array would provide more performance.

The only tim I would use two seperate arrays is if one database was read-heavy and the other write-heavy, then with some controllers it is possible to tune the read/write ratio of each cache or to assign all the cache to one array thus speeding up that database at the expense of the other.
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