What do you guys think about this?

[Galland1928]

Ok, I work in the IT department of a small, but very fast growing company. Before I started, they added new servers for a new software package that was purchased. All of the systems have pretty decent specs. Our SQL database server is the only one that makes me question why.

We will be running SQL Enterprise 2005 on it and will probably have a database somewhere between 5-7GBs to start off with.

It is a HP DL580 1 3Ghz Xeon MP (Quad capable) 12GB PC2100 RAM and 3 RAID arrays.

That sounds alright, but they are RAID 1 arrays. In fact, every server they purchased is running RAID1 (our old process manufacturing/database/file/print/card processing server is running software RAID 1) besides our Exchange server (RAID 5) Now I know a decent amount about RAID but no reason whatsoever to go with RAID 1 for a database. (two of the arrays are running 173GB 15k drives)

Does anyone have any clues as to why this would have been done??

 

[BrownTown]

maybe they think that this information is very important and wan't to make sure that it won't be lost? With RAID 5, a 2 disk failure means you loose the whole array, even with RAID 6 it only takes 3 discs. Maybe a small fire or something comes and kill several discs, or something like that and then you loose everything, with RAID 1, you only loose information if both mirrored discs are destroyed ,and you still only loose part of the information, not all of it.

 

[Galland1928]

Well, the thing is, the RAID1 arrays themselves only consist of two drives for each array. So two can go bad here too.

ALso, with RAID1, there is no error checking right? (unless HP has something in there that isn't standard) RAID5 though would have error checking.

 

[BrownTown]

wait, are you saying that the whole array is only 2 disks?, in this case RAID 1 and RAID 5 use the same amount of space, so RAID 5 can no longer claim any advantage spacewise.

 

[Matthias99]

Originally posted by: Galland1928
Well, the thing is, the RAID1 arrays themselves only consist of two drives for each array. So two can go bad here too.

ALso, with RAID1, there is no error checking right? (unless HP has something in there that isn't standard) RAID5 though would have error checking.

RAID5 includes parity checking, but it's not usually checked on every I/O (as this would *destroy* performance, dropping it well below that of a single drive). For similar reasons, RAID1 integrity is also not usually checked on every read (though it sometimes is an option depending on the controller). Usually there is a 'consistency check' option you can run to verify that either a RAID1's mirrors match, or a RAID5 has correct parity information for each block.

RAID is primarily useful in terms of maintaining uptime; it is NOT a replacement for regular backups (since, as noted, your building could burn down, or multiple drives could fail, etc. etc.) I would presume it was done to minimize the chance of a random hard drive failure taking down your database server. With a hot-swap RAID1 or RAID5 controller, you can just stick in a new drive and keep running.

 

[Galland1928]

Whats written to one drive is written exactly the same to the other, whereas RAID 5 you would have possibly only 1 or 2 drives (depending on the array size) that could get errors. RAID 1 is limited in size by the smallest hard drive and can never be upgraded in size whereas with RAID 5 you can start out small and add hard drives over time.

On the backup side of things, we have a dedicated backup system and everything is backed up every night so whether it be RAID 1 or 5 we will always have a backup of it.

I still don't see why they would have chosen RAID1 over RAID5. Wouldn't a database server at a fast growing company need at least RAID5?

The reason why I"m asking this now is because we havn't gone live with this system so it is still in the testing phase so being that I took over, I can change this if I want to.

 

[BrownTown]

now im confused again, you said that you only have two drives, so RAID 5 wouldn't make sense, if there are more then 2 drives then RAID 5 is a good idea. But if you currently have 2 and are thinking about upgrading to more then you can switch from 1 to 5 on the upgrade, either way you're going to have to rebuild the array when you add the extra drives...

 

[Galland1928]

3 arrays, 2 drives per array, and each array is RAID 1

 

[Galland1928]

I just want to know if anyone else things it would still be worth the time and investment to upgrade to RAID 5?

 

[Loki726]

Originally posted by: Galland1928
I just want to know if anyone else things it would still be worth the time and investment to upgrade to RAID 5?

If you don't need any more space right now, I would say just leave it. If you ever need more space in the future (and have a raid5 controller to spare) just remember that you can switch to raid 5 and get potentially faster performance and 2 extra drives.

 

[alzan]

I don't have any stats to backup my claim, but I believe RAID 1 will give better database performance than RAID5; I believe it has to do with the fact that a RAID5 has to create the parity information, giving you a performance hit.

If that's true than no it wouldn't be worth the investment (time or money.)

alzan