

Usable storage for cloud storage - MrGeeky
http://serverfault.com/questions/270002/calculating-physical-to-usable-storage-for-open-stack-swift-object-storage

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notmyname
Copied from serverfault:

Since you are looking for storage numbers, I'm assuming you are referring to
swift, openstack's object storage system.

Swift by default stores 3 replicas of the data. This means that total storage
/ 3 is your billable or usable storage. The number of replicas is configurable
on a cluster level.

However, you can get more detailed. I'd recommend you keep your drives at less
than, say, 80% capacity to allow for sudden bursts of storage needs and to
give you time to acquire new hardware and grow your cluster. Also, keep in
mind that every 2TB the manufacturer advertises is only 1.82TB. Then you have
some overhead for formatting.

The above gives you "total raw storage" * 0.90949470177292824 * .8 / "replica
count" = "billable storage".

Plugging in your numbers, we get 96TB * 0.90 * .8 / 3 = 23.28TB billable.

