advise on raid level needed

we have a 2003 server that runs a database accessed by 20-40 members of staff via pc's and laptops. All are xp pro pc's
the server has two 70gig scsi drives. I was thinking of a implementing raid 1 in order for disk 1 to mirrored thus the have fault tolerance. however will having raid 1 decrease the read speeds of the drive, what would you guys recomend?

thanks as always
exdosAsked:
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Lee W, MVPTechnology and Business Process AdvisorCommented:
RAID 1 SHOULD increase read speeds.

I would suggest reading over this link:
http://www.pcguide.com/ref/hdd/perf/raid/concepts/perf.htm

And these recent discussions (which are related).
http://www.experts-exchange.com/Storage/Q_21727036.html
http://www.experts-exchange.com/Storage/Q_21729410.html
arnoldCommented:
Do you have a RAID card or are you implementing the mirror configuration using software?
In any case, your choices are limited by what you have.  mirror is the only solution available to you for some fault-tolerance.
RatOmeterCommented:
leew is wrong. Raid 1 (mirroring) DOES NOT and IS NOT designed or intended to increase data access time. Its purpose is redundancy only.  Raid level 1 will likely decrease access time by at least a small amount, but how much depends on the RAID hardware used (if any).  If you are using Windows software to impement mirroring, expect more performance degradation (though generally slight).

Please check this link to a google search:

http://www.google.com/search?hl=en&lr=&safe=off&q=raid+performance+redundancy&btnG=Search

RAID 0+1 and RAID level 5 have each saved my @ss in real life.  Please read and understand what the various RAID levels are and how they might be combined, it could save your's as well.

I'd say that "for free advice, you get what you pay for," but you're paying for this, aren't you?
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RatOmeterCommented:
correction:

"increase data access time" should be "improve data access time"
Lee W, MVPTechnology and Business Process AdvisorCommented:
So, RatOmeter, you disagree with the following statement?
"Read performance under mirroring is far superior to write performance... There's absolutely no reason to access both drives; the controller, if intelligently programmed, will only ask one of the drives for the data--the other drive can be used to satisfy a different request. This makes RAID significantly faster than a single drive for reads, under most conditions."

I would suggest you review the following link:
http://www.pcguide.com/ref/hdd/perf/raid/concepts/perf.htm
It's where I got the above statement.

Would also be good if you filled out your profile so we have some perspective on your qualifications and can weight your responses.  (I've definitely been wrong before and I'll be wrong again, but I don't think I am in this case).
DisorganiseCommented:
Actually, RatOmeter is wrong.  RAID 1 *CAN* improve READ performance - though I suspect the quality of your controller comes into play somewhat, and using the OS to perform redundancy will always incur a performance penalty over dedicated hardware.

Ultimately this is what RAID1 was designed for: redundancy + improved READ performance since either disk is able to supply the next block - ergo, if one disk is half a rotation nearer, it'll be quicker to read from that disk, which reduces the latency over a single disk system.  Since a WRITE must be duplicated to both disks, there may be a slight degradation in performance depending upon your controller card.

Here are some threads to back up my statement and satisfy your research:
http://www.real-storage.com/raid-1.html
http://alumnus.caltech.edu/~rdv/comp-arch-storage/FAQ-1.7.html
http://www.acnc.com/04_01_01.html
http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci214332,00.html
http://www.webopedia.com/TERM/R/RAID.html

There's a million others of course and they all say the same thing.  READ performance is increased with (hardware implemented) RAID 1.

With the number of users you have, I don't think you'll have too many issues.  Separating the OS, Database and Database transaction logs is always a nice idea, so if you *can* get another pair of disks, I'd create a 2nd RAID 1 set and move the DB to it (leaving the logs and OS on the original RAID 1 set - preferably in separate partitions to avoid the log file filling up the OS drive letter).  Separating in this manner will, in my opinion, yield better performance than placing the 4 disks in raid 01 or 10 due to less contention.

If 2 disks are your limit, then I'd advise to partition off around 18GB for your OS and pagefile and put the logs and DB's on the other partition.  Again, this results in the database application (SQL?) stopping itself when the partition fills up (perhaps due to broken back-ups so logs aren't truncated) but doesn't take the OS out with it.

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RatOmeterCommented:
I must humbly submit that I was in error in so strongly asserting my position.  Upon review, I see that leew and Disorganise are correct that hardware RAID level 1 implementations usually result in a gain in read performance as well as the design intended redundancy. There are some caveats that may apply to certain hardware/software configurations, but probably do not apply to exdos's situation.

Some hardware IDE RAID implementations (as well as software only) will see little, if any performance gain at RAID level 1 if the harddrives are attached to the same controller (ie both on the primary or secondary port).  I realise that your (the Author) configuration includes SCSI drives which presumes the need for a specialised, hardware RAID controller which may be free of any performance hinderances. My own personal experience with RAID 1 involved a HighPoint brand IDE based chipset with a single drive on the primary and secondary ports each in a Windows NT 4.0 environment.  Extensive benchmarking with large SolidWorks projects indicated a negative performance gain in this configuration. I see now that this experience has blinded me to the results of the book studying I did prior to that.

Carry on as if I hadn't bothered you

PS: leew, I updated my profile somewhat, not that it helps me in this thread.
durindilCommented:
Actually, you are BOTH right, but it is because of what Disorganise suggests, it is in the controller.  Most of the "fakeraid" controllers, such as the majority of the SATA controllers, can NOT access both drives at the same time.  The enterprise controllers, Fibre Channel, most SCSI, and the high end SATA controllers, have separate processors that can control the drives apart from each other.
David_FongCommented:
If you take the two drives and make them into RAID 1 it will slow it down, if you buy two more disks it will either stay the same or speed up but as durindil says it's dependant on what controller you have.
Lee W, MVPTechnology and Business Process AdvisorCommented:
exdos - any reason you didn't split the points...?
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