Considering RAID 0 or RAID 1?
Hello and welcome to my User Tip.
We get a lot of questions about RAID (redundant array of independent disks) and what it's for, some are using as backup methods, so I will give a general outline and why RAID 0 and 1 are NOT good for backups.
There are many types of RAID, however I will cover just RAID 0 and RAID 1 here as that's what Disk Utility can format.
Other forms of RAID are extremely good means for backup for large data, video etc., and those sort of people turn to the professionals at places like MacGuru's.
RAID 0
This array of drives uses two or more drives of the same model and speed to split the data path from the computer to read and write to all the drives at the same time with one copy of the data. The more drives, the faster the RAID 0 is.
So if there is five drives in the set, the first byte of data goes to the first drive, the next byte to the next drive and so forth and starts all over again. This has a effect of being incredibly fast read/write speeds to the limit of the interface, computer, operating system, or program can handle with enough drives.
Dangers with RAID 0 is that any failure on any of the drives in the set, or a cable, corrupts the data path as it's fragmented and thus the data fails on all drives in the set. So RAID 0 is incredibly dangerous for permanent data, anything on it needs to be backed up as soon as possible to a more reliable single spindle drive or other more stable backup system.
However the extreme read/write speed is beneficial for certain uses where large data needs to be transferred quickly, or large files being worked on.
SSD's are currently topped out about 1TB in size now, but for larger needs one may have to use larger hard drives and some sort RAID 0 + backup for move huge data around in a short time period.
If one has the benefit of time, then setting up the transfer between more reliable +1TB hard drives in the off hours and coming back in the morning would be ideal.
For most users, a external or internal Solid State Drive is better choice as it's faster than traditional spinning platter hard drives which RAID 0 was intentionally for to overcome it's speed limitations.
Apple will not allow OS X to be installed on a RAID set, so forget about going there to speed up your machine, get a SSD instead.
For the curious, I have installed OS X via cloning on a RAID 0 set before, it boots and all, but OS X goes through a setup process and that takes a set amount of time regardless if the data is immediately available from the boot volume. So stick with a SSD as its more reliable than RAID 0.
RAID 1
RAID 1 consists of two drives in the set, the data path is sent complete, duplicated (not fractured like in RAID 0) to both drives at the same time, so both are written to with the same data at once.
Some chose this as a backup option thinking it's going to protect them from a drive failure, which it will but only partially.
People who have used this method as backup and had one drive fail, found out the remain drive is non-accessible. Sure the data is on the drive, but because it's half of a set it doesn't register as one drive to get at the data. Complicated steps are required to fix this and get at the data or third party software like Data Rescue, which bypasses things and reads the bits on the drive directly to attempt recovery are used.
Other problems with RAID 1 as a backup method occur when there is a software problem, accidentally deleted files or corruption, it occurs to BOTH drives at the same time in a RAID 1 set.
So RAID 1 doesn't make very good sense as a backup option for nearly all users because it doesn't give one the benefit of time.
There are some professional use cases where the data is so darn vital that it be copied immediately upon receiving (like ET calling) that a RAID 1 makes sense, but for a lot of common users of Mac's and most all PC's users, RAID 1 is a poor choice as a backup option.
The reason I write this User Tip is because many geeks and computer types think they know what they are talking about and sling around RAID 1 as a backup solution to those who come here.
Other options?
For RAID 0, use a SSD instead. Single drive, fast and reliable, no headaches and need for immediate backups.
For RAID 1, use cloning software like Carbon Copy Cloner or SuperDuper with their built in timed cloning to make a update. This provides software and hardware protection of data, giving one the opportunity to fall back onto a earler version or recover deleted files they just Trashed.
Another option for most new computer users is OS X's built in TimeMachine, which provides a means to go back and retrieve files for a limited time.
Most commonly used backup methods
So hopefully this user tip will assist in answering this rather lengthy question that some come here with when they ar econsidering RAID as a backup system.
Any more detailed information can be found at Wikipedia and other locations online using search engines.