Winston_Churchill wrote:
Finray wrote:
Winston_Churchill wrote:
Theres a difference? I've never done RAID before... whats the difference between the two?
Raid 0 is when you have two hard-drives. Windows sees them as one. For example, if we use two 500GB drives, Windows will see these as 1TB. When writing files to these hard-drives, it will write half the file to one drive, and half to the other drive, in theory doubling read/write speeds.
Raid 0+1 is when you have three drives, and have two set up as is in Raid 0. The third drive then copies one of the Raid 0 drives. If a disk is to fail, you only need half the information (when reading through the backup drive, it can take any '1' and realise on the other drive the corresponding binary digit would have to have been a '0'.)
You didnt answer my question. I asked for the difference between 0+1 and 1+0.
1+0 is striping a mirrored set, 0+1 is mirroring a striped set. With a normal RAID controller you shouldn't see a performance difference between the two, but there is a difference in fault tolerance and rebuilding times. This is because the RAID logic begins in the base set, and because the base set is oblivious to the existence of any sets above it.
Imagine a disk-loss scenario in a storage configuration as the one suggested, four disks in either a striped mirror or a mirrored stripe. In a mirrored stripe, 0+1, when you lose a disk from your base stripe, your array falls down and goes boom. You'll need to power down and consult your local RAID utility to rebuild your stripe from your mirrors, as you can't write to the broken stripe when this happens. This also means that in the absence of a cold backup drive, you'll have to rebuild your RAID array using your functioning mirrors as the base stripe in order to get back up and running.
With striped mirrors, 1+0, when you lose a disk from either of your mirrors, then, well, it's like losing a disk from any other mirror. You can still write to both mirrors, which means that you still get to finish your work before shutting down to address the issue. In this case, if you don't happen to have a disk on hand, and don't mind the risk, you can run your damaged mirror just fine until your replacement drive arrives.
This is all enough reason to pick striped mirrors over a mirrored stripe in a four-disk storage configuration, and the pains of rebuilding a mirrored stripe obviously only increase with the size of the stripe being mirrored.