hard drivehard-drive-failureraidraid-10
In a 4-drive RAID-10 setup, how many drives can I "safely" lose before the data becomes unrecoverable? It's a bit unclear to me whether the setup provides one drive or two drives worth of redundancy.
Is the redundancy of RAID-01 different or the same as RAID-10?
A RAID-0 configuration utilizes 2 separate hard disks and writes "chunks" of data to each one to minimize actuator movement and read/write data faster (each arm does half the work in a sense). The caveat with this is that there is a lack of fault tolerance - if one drive dies, all of your data is gone. And since there is 2 drives handling your data, the chances of losing your data is basically doubled. You may want to look into RAID1+0, which give you speed benefits as well as fault tolerance. You can swap in another disk upon failure and have the other disks rebuild it.
The RAID-0 image from wikipedia domonstrates it well:
imagine the disks are showing a file called A.txt. Now, imagine each section as a 4096-byte cluster for example. Each disk is holding roughly 16384 bytes of this text file, and if one disk dies, there is no way to recover the other half.
If you are limiting yourself to 2 disks, I'd suggest only doing the RAID-0 configuration on the operating system. Any files important to you should be stored on separate media such as an external drive, or if it was a possibility, 1 more hard drive. If it meant the difference between having a fast machine without fault tolerance, or having a slower machine with my files safe, I'd choose a slower machine. For me at least, I'd rather be safe than sorry.
From:
http://forums.nvidia.com/lofiversion/index.php?t11732.html
PS : During this, i had to redefine the boot disk, bios config was lost, but don't know why.
Best Answer
RAID-10 consists of a stripe of mirrors. As long as one disk in a mirror is functional, you're fine.
If in the below example you lost Disk 0 and 1, you would lose data. If you lost Disk 0 and 2, your data would still be accessible from the mirrored stripe.
Picture from Wikipedia.
Since RAID-01 is a mirror of stripes, it offers the same redundancy. The disks are just logically ordered in a different way.
In practice, this means that you should already be warned when one disk fails, because the second disk failing may have a one in three chance of being the one that makes you lose data.