Sizing Object Storage Honestly — Raw × 0.6 Is What You Can Sell
A customer asks for 100 TB of S3-compatible storage and the first draft of the design shows 100 TB of disks. That design is short by two thirds. Erasure coding takes about a quarter, a sane fill limit takes another fifth, and what you can honestly sell is roughly raw × 0.6. Here is the method, the hardware rules behind it, and the commands that prove the numbers on a running cluster.