How does nimble calculate min. usable capacity for the arrays?

[jliu79]

I'm just curious if anyone knows how the minimum usable capacity is calculated for an array. For example, on their website, a 72TB(12x6TB) raw disk capacity array's minimum usable capacity is 50TB. I know Nimble uses RAID-3P which is triple parity with no dedicated spare, I feel like this way the minimum capacity should be bigger than RAID6 with spare which has 72-(6x3)=54TB minimum capacity.

[#2]

Jason- Good question.  Nimble's minimum usable capacity would be RAW storage capacity minus RAID overhead (triple parity/three drives) as you stated.  Then there is some small system overhead, which accounts for the other 4TB "missing" capacity in your calculation, using the 72TB example above.  As an example of miscellaneous system data that can't be counted as capacity, there are multiple redundant copies of the Nimble OS.

[jliu79]

Thanks Ed for the explanation.