RAID Options with (3) 1TB drives

Question

Hi Folks,
Setting up a brand new XServe with Snow Leopard. I have (3) 1TB drives, as well as the 128GB SSD for the OS. Can anyone recommend the best configuration for the setup of these 3 drives? Srtiped or Concatenated? RAID 1 or 5?
Thanks in advance,
-andy-

Answer 1

No one can recommend a setup other than yourself, since you're the one that knows what you plan to do with the server. All anyone here can do is tell you the pros and cons of the various options.
First off, RAID 5 requires a hardware RAID card - you can't do RAID 5 in software alone, so unless you also have the RAID card that's not an option.
RAID 0 (striping) gives good performance and results in a volume approximately the same size as all drives combined - so three 1TB drives will yield about 3TB of usable space.
There is no redundancy in RAID 0, though, so if one drive fails all the data is lost because each file is 'striped' in chunks across all drives
A concatenated array is similar except that each drive is just appended to the end of the previous one. It offers the same usable capacity as RAID 0 (e.g. three 1TB drives ≈ 3TB space), but offers lower performance (since you can't parallelize the reads/writes over multiple drives. There's still no redundancy but there is a higher chance of recovery if a drive fails (the data on that drive is gone, but data on the other drives may be recoverable).
RAID 1 mirrors data across multiple (usually 2, but can be more) drives. Data written to disk is written to all drives simultaneously so the loss of one drive doesn't affect availability (the system keeps running off the other drives). Performance is lower than RAID 0, but you gain the redundancy.
Available space is based on the smallest drive in the set, so using any number of 1TB drives in the array will result in a 1TB usable volume.
So that's the back-end. It's up to you to determine which is most appropriate for your setup.
For example, if performance is your primary driver, then striped may be the way to do, as long as you have a viable backup strategy for any data you wanted to keep.
Striping may also be viable if available capacity is your concern - if you need 3TB of space then this is pretty much your only option.
However, if redundancy is your concern, then mirroring seems more appropriate as long as your needs are less than 1TB. It doesn't necessarily make sense to mirror three ways, so maybe you mirror two drives and use the third for backup.
Or maybe you need redundancy and capacity, then maybe you need the hardware RAID card to go RAID 5 (this will yield 2TB usable space, with redundancy to protect against single disk failure).