Unfortunately, this information is not 100% correct (I've taken A+ courses, and I have despaired at the information in some of the books- I've also taken MCSE courses and not been overly impressed with some stuff in there too).
In RAID 5, you are not limited to the capacity of ONE drive. If you have X drives in an array, you have X - 1 drives' worth of capacity. For example, with 3 500GB drives, you will have 1TB worth of capacity. 3 drives (1.5TB), with the equivalent of one (500GB) being used for parity. (Wait... looking back over your explanation, you have it right, but typed "one" instead of "two".)
A little information on some more popular RAID levels:
If your data (in chunks of D1, D2, D3, D4, etc.) and parity (P1, P2, P3, etc.) are written to the arrays, you end up with the following:
RAID 0- data striped across all drives:
Drive 1: D1, D3, D5
Drive 2: D2, D4, D6
Lose one drive, you lose it ALL. This is pure speed, no redundancy or fault-tolerance.
RAID 1- No parity, just mirroring:
Drive 1: D1, D2, D3, D4, D5, D6
Drive 2: D1, D2, D3, D4, D5, D6
Lose one drive, you lose nothing. This is just redundancy, no increase in speed (actually a slight hit).
RAID 4: One drive of the array (3+ drives) is used for mirroring, data striped across the rest:
Drive 1: D1, D3, D5
Drive 2: D2, D4, D6
Drive 3: P1, P2, P3
Lose one drive, you can still survive.
RAID 5: Like RAID 4, but everything is striped:
Drive 1: D1, D3, P3
Drive 2: D2, P2, D5
Drive 3: P1, D4, D6
Again, lose one, and you're still in business. This is more fault tolerant than the others.
Generally, unless you REALLY needed a huge single drive array, I would recommend against RAID 5 for most people. The complexity and cost is rather high; better to invest in a next-gen DVD drive (like Blu-Ray or HD-DVD) or a mega capacity backup solution. Newegg.com - LITE-ON 2X Blu-ray Disc Triple DVD Burner Black SATA Model LH-2B1S - Retail |