how does the math work out there?-superboyac
Here's a simple explanation:
Let's say you have four, 2 TB drives. You would designate one of them as the parity drive, e.g.,:
D1 (2 TB)
D2 (2 TB)
D3 (2 TB)
P1 (2 TB)
This would give you 6 TB of data space with 2 TB of parity. The simplest way to envision this is with math, i.e., 1+2+3=6 (D1 = 1, D2 = 2, D3 = 3, thus, P1 = 6). If you lose any one of the "D" drives, you can easily calculate what you're missing. Let's say you lost D2 and have replaced it. The system starts to rebuild based data off the P1 parity drive information like this:
1+?+3=6
Obviously, ? = 2. Yes, this is a 50,000 foot view, but does that help to explain things? Also, if you were to lose two drives at one time, you wouldn't get all your data back (unless you had
two parity drives). In other words, you can simultaneously lose as many data drives as you have parity drives. So goes the theory, anyway. YMMV.
