Raid 1 / Raid 5 - disk capacity

[Jill Turner]

If I require 100gb of usable disk space how much would I require altogether if configured in raid 1, and if configured in raid 5, is there a certain percentage that is uses up.

[Mark Poeschl_2 · Accepted solution]

RAID1 requires double the raw capacity so to get 100gb usable you'd need 200 gb raw. RAID 5 is a little harder. It depends on how your storage controller (or you for older manual controller types) builds your RAID sets. If you built a three spindle RAID5 volume you would get 2/3 of the raw capacity. If you built a six spindle RAID5 volume you would get 5/6 of the raw capacity. It's an N+1 sort of thing.

Also - whenever calculating disk capacities bear in mind the hardware 'tax' on usable capacity. When a H/W vendor sells you a 100 GB disk you get 100,000,000,000 bytes of raw storage capacity. S/W capacity calculations generally think of 100 GB as 100x1024x1024x1024 = 107,374,182,400 - a 7% discrepancy. (The 'tax' goes up to 10% if you start working in terabytes.)

[Jill Turner]

Thank you for the quick response it has helped me a lot.