Quote:
Originally Posted by james... 
Assume I know nothing about raid.
Obviously I know how a hard drive works, so you can assume that.
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Hmm. How a hard drive works is considerably more complex than RAIDing them together...
Wikipedia is a good place to start, but even more simply you can look at RAID as a way to overcome some of the disadvantages of hard drives. You use different levels (or types) of RAID to overcome different disadvantages, and each level has it's own pros and cons.
Very briefly, the common levels:
RAID0 - writes little bits of data to more than 1 disk in turn. As a result you get higher speeds, as you read/write data simultaneously to multiple disks. You also get higher capacity, as you get multiple disks presented together as 1 drive.
The disadvantage is the higher failure rate - one disk dies, everything goes.
RAID1 - mirrors 2 drives so both hold the same data. Main advantage is you keep your data if one drive fails. Disadvantage is it costs twice as much (have to buy 2 disks) for no increase in capacity and no real performance change.
RAID10 - a combination of RAID1 and RAID0. Needs 4 disks, offers the advantages and disadvantages of each.
RAID5 - Writes chunks of data to each disk as in RAID0, but now also writes a little bit of data that can be used to recalculate any of the other bits in each chunk. Means if a disk fails you can still use the array. Often seen as a 'best of both worlds' between RAID0 and RAID1, as you get better performance, some failure tolerance and still retain high capacity, although in reality it is much more complex than this. You get the capacity of all but one of your disks added together. The main disadvantage is the high cost of the controller and high overheads for certain operations.
RAID6 - like RAID5, but can survive 2 disk failures, but at the capacity loss of 2 drives.
That will do for starters, you are better off reading wiki and asking some more specific questions than having people try and explain RAID entirely...
Note that this quick post ignores things like using different sized or mismatched disks and doesn't really go into all the pros and cons for each level, but is just a quick intro...
(Note also that RAID0 is not really a RAID level at all - see the above post for the RAID definition - no redundancy here, so not really RAID at all, but it's the most common level you will see on this forum at least...)