Basically, in RAID 1, you have two identical hard disks, each with all the data on it (they are both exact copies of each other, so if one fails then you still have all your data on the other hard disk. Windows see's the two hard disks as one, and the data is duplicated between the two of them, giving you a lot of redundancy. However you do only get half the space (if you had two WD 640GB disks, you would get 640GB of space, with everything stored twice.
In RAID 5, (sorry i made a small mistake in my last post:STUPID
you need at least 3 disks, and (this is where my mistake was:
OMGyou get [Number of drives - 1 * size of drive] space. So for 3 * WD640GB drives you would get 1280GB, or 1.28TB of space, and for 4*WD640GB drives you would get 1920GB or 1.92TB or space. Mybad!!.
The data is striped across two(or if you have more...) of the drives (split up, and a bit of it sent to each drive), with a parity on the third(or forth...depending on how many drives you have). The parity is what is on the other drives summed up. This leaves the drives (and excuse my bad paint) looking a bit like this:
Therefore if one drive fails, the RAID controller can use what is in the working half of the data, and the Parity of the data to work out what was in the failed drive, and copies it into a new (replacement) drive. For example if drive two were to break, for block A, the first half would be compaired to the parity, to rebuild the data on the second half of block A, and copy it onto the new drive, meaning that all your data is safe.
It has the advantage of being faster, as it gets half the data from each drive, so you do not have to wait so long for the drives to read and transfur the data, and it is more practical than RAID one, in that you get more of the space, only losing the size of one drive, compaired to RAID 1, where you loose half the space.
Hope it is OK and helps
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