On Feb 11, 2012, at 7:29 AM, Jorge Luiz CorrĂȘa wrote:
> 
> 2) About Swift, how do I determine the total usable storage capacity of the 
> system? For example: I have 3 nodes with 5 HDs of 1 TB each one. Straightly I 
> have 15 TB of space. If I use raid 1 I can say that I'm going to have 7,5 TB 
> of usable space. And with Swift, is it possible to determine this usable 
> space? 

Here's how to find the usable space for swift

marketing size of the drive (eg 2TB) * .92 (to account for formatted size * .8 
(for 80% fullness) / replicas

If you have 15 TB of formatted space with 3 replicas, that gives you 5TB of 
usable space. If you have 15TB of unformatted space with three replicas, that 
gives you a little less than 4TB of usable space.

The reason I calculate it at 80% fullness is so that you have some headroom to 
expand as your cluster grows. You don't want to have your hard drives fill up 
completely before you decide it's time to buy some new ones.

--John

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