Discussion on:

Learn the differences between RAID levels

redundant array of inexpensive disks

I have used both SCSI and IDE cards and prefer SCSI for the added capabilities - hot swap, drive blink, etc.

The problem and warning I have is to watch out for IDE controlers and ATA-100 drives. some controler cards cannot handle ATA-100 drives, so you need to step them back to ATA-66 or 33 to work. No need to waste money on high speed drives if your card cannot handle it.

Make sure you quiz the card vendor on the acceptable speeds and mention the drive by vendor name when you do. Some drives don't work as well as others, a lesson I learned the hard way.

You are not limited to a single RAID level within a system. For example, my mission-critical MRP server will have 6 15k-rpm SCSI drives, hot swappable. 3 in RAID-5 for the main data volume. 2 in RAID-1 for the system/boot volume. and 1 standalone for the swap file. This gives the minimum complexity, and the maximum fault tolerance. With the RAID arrays implemented in hardware, even on the RAID-1 if a drive dies, I can hotswap it out and rebuild on the fly, without so much as restarting the server. Sweet

I'd have liked to see more in-depth information about what RAID to use in what situation. The article doesn't provide much else save for a listing of the possible RAID types. Perhaps a future article can elaborate?

It depends on your level of paranoia and performance needs. All RAID types are inherently slower than a single drive, you need to decide how much of a slowdown you can handle. I have found that by using an add on RAID card that performance hit is negligible.

For example using the three most used (and cheapest) types: 0, 1 and 5.

0: Disk Stripe ? Space consolidation is all this is good for IMHO.

It has no fault tolerance but does not slow you down as much. If one drive goes down, you lose data. I really don't know of many times this is used, but if you needed to place a logical drive onto two physical drives and get the total space from them, this is what you would use. Two 1 gig drives yield 2 gigs space.

1: Disk Mirror ? Operating System files redundancy for fast system recovery in the even of a drive failure.

Slow writes, fast reads. This is fault tolerant, if one drives crashes, you can run off of the second drive. I have used this for boot partitions in NT. If my "primary" drive goes down, I have a floppy with the boot.ini (and other system partition files) handy that will bring the system back up on the "secondary" drive. This RAID can be extrapolated up to even mirroring controller cards then the drives to provide redundancy of controllers too. You only have the space of one drive though. Two 1 gig drives yield only 1 gig of space. (FYI: In NT the system partition contains the files used to boot the OS, the boot partition contains the Winnt directory and the OS files. Bill must have been smoking something that day.)

Continued...

5: Disk Striping w/parity ? Data files fault tolerance if a drive goes down.

Slower performance, but if a drive goes down, all you need to do is pop in another drive and the system will rebuild your data from parity info. I?ve used this for storage sets intended for mission critical data; where we store all the stuff that makes us money. This doesn?t mean you don?t have to do backups though. If you lose two, you?re out of luck. It provides some space consolidation, but you still loose some to the parity data. Four 1 gig drives yield 3 gigs of space.

Hope this helps.

Yes, this does help to clarify things. Thanks for sharing these examples.

Your total storage expectations, to the degree that you can see the future. Servers have limited bays, scsi cards support limited number of devices. At some point adding one more disk becomes an expensive proposition. Changing from one raid level toanother if you change your mind is not an insignificant task in many cases, so try to get it right the first time. Not necessarily easy choice. Struggle with it too each time.

I was curious with the response that a single drive is faster than RAID 0. This maybe because there are 2 types of RAID 0, Stripe and concatenation. With stripeing the system writes a block of data to the drive, normally 128k for scsi drives, and the next block it writes to the next drive in the RAID group. If you put each of these drives on different controllers/scsi cards it should out perform a single drive. The other version of RAID 0, concatenation will only move onto the next drive once the first drive is full. This is normally used in situations where you are about to run of space.

With all the RAID levels there is always a trade off.
RAID 0 (Striping) more performance but less resilience
RAID 1 (Mirroring) more resilience but less performance and greater cost. Normally about 25% performance loss and you need twice as many drives.
RAID 3/5 (Striping with either dedicated or distributed parity) Resilience, lower cost than RAID 1 but substantial lower performance.

Mostusers go for RAID 0 + 1 which gives then the resilience and performance, but at a cost.

I'm trying to arrive at the optimum RAID strategy for a Business Intelligence server when cost is not an issue:

There will be 3 RAID arrays, each with their own controller, for OS, Application, and Page File. What is the best RAID strategy for each array?

Environment is Wintel...Thanks!

There are more possible answers then can possibly be explaned in this format but the most likely answers I would choose follow.

For the OS I use a mirrored drive (RAID 1)That is the only available softawre answer (that I`m aware of) and dispite other thoughts in this discussion I use to replace OS backups.

For the application there are many other possibilities depending on how critical the Ap is but RAID 5 is likely the correct answer.

For the Page file I`d use RAID 0 because fault tollerance isn`t important on that (for my purposes at least.)

I`d really give this some thought before blindly following my suggestions though...your circumstances may be different then myne.

I think you need to cut out the damned ad that is blocvking reading the grid -WTF??? Internet is for information not to sell!!!!