Question about RAID

RAID stands for Redundant Array of Independent Disks. That is, it consists of an ARRAY of (SEVERAL) separate HDD's. One should never even try to create a RAID array from separate Partitions on one HDD unit - even if the RAID system would allow that, which I doubt.

There are quite a number of different RAID systems available, each with different applications, requirements and performance features. RAID0 splits the data between two HDD's and can speed up performance because it shortens the delays for head movement seeks. However, it MUST have both units working, or ALL data on the system is lost - and the probability of that is double the probability of losing one HDD. RAID1 duplicates the data on two HDD's so that, if one fails, the other can keep on working with no downtime - but you need to repair it soon to restore the feature. RAID5 uses 3 or more HDD's and distributes the data over them all, along with a calculated set of checksums. The extra calculated data is such that, if one HDD fails, the remaining good data allows all of the missing data to be reconstructed. This security system takes extra time and is slower than some other systems. RAID6 does a fancier version of what RAID5 does, and it can recover from the simultaneous loss of two of its several (often 6) HDD units. There are other systems like RAID0+1 and RAID 10 that offer different features.

To use a RAID system you need to understand the benefits and risks of each type, and the costs in money and performance. One thing to understand for sure: RAID is NOT a substitute for a backup system!! I once experienced a failure of a RAID5 system - the one that can "fix itself" - when two HDD's failed at the same time. This was in a professionally-run shop that had reliable backups and they restored from there - in three days, because it was a big busy server working 24/7.