New to RAID and redundancy

Question

I just purchased an HP Proliant DL580 G2 server. I have never used RAID, but this system comes with:

Smart Array 5i Plus Controller (integrated on system board), Dual Channel, Ultra3 (supports RAID 0, 1, 1+0, and 5 across internal hard disk drives) with 64 MB of memory.
64-MB total memory for code, transfer buffers, and read/write cache on the 5i Plus Memory Module
Connector for Battery Backed Write Cache (BBWC) Enabler

And the server comes with 3x36GB hot-plug SCSI drives. I want to set this server up to host a fairly simple PHP web site and accounting system I'm creating (mysql backend), basically an intranet site. It will never get anywhere close to 36 gigs, however I do need it to be VERY reliable. I plan on running Debian 5 Lenny (php/lighttpd/mysql stacj) on it. I figured if I put all three disks in a RAID-1 mirror array, it would allow for me to have two spares in case of a drive failure. It also has redundant power supplies in case of a failure on that front. Is there anything special I should know about configuring the raid this way, or should I be going for a different type of raid? Any help would be greatly appreciated. Also, any advice on redundancy in general on a server of this type would be appreciated as well.

Thank you so much.

Not looking for super-performance out of the RAID, just mostly for redundancy.

Answer 1

If you use RAID1 (which is not a bad idea at all) you would end up having one spare, as the RAID1 array uses two drives (mirrored).

Another alternative would be RAID5, which requires 3 drives to start off with, leaving you no hot spares.

Both of these RAID configurations can run in degraded mode (i.e. if one of the hot drives fails), and since you have hot-plug drives, you can easily get yourself a spare and swap out the faulty drive without having to power down the server.

There is a debate possible over what is better in this case. I am not going to get involved in that debate. I would recommend you read the wikipedia page on RAID arrays and then make up your own mind.

Answer 2

RAID1 is a good idea for a three disk setup. You would build a RAID1 array, select 2 drives, and then configure the third drive as a hot spare.

Its also worth noting that you could do RAID5, but I feel that its an overly-complex solution for your needs and comes with a read performance hit. Also you won't have room for a hot spare as it will require 3 disks.

Considering disk space isn't an issue, I'd stick with RAID1.

Answer 3

RAID6 + hot spare is a decent compromise between storage size and redundancy. Why RAID6 and not RAID5? It's very probable that if you buy hard drives that were manufactured at roughly the same time, two of those drives would likely fail at the same time (unfortunately, I don't have the stats/probability chops to back this up.) With RAID5, you'd be boned, even with a hot spare. With RAID6, this will only inconvenience you at 3 AM.