You want to give each user a fixed amount of storage. But most users don't use anywhere near their total. So you oversubscribe to save money by pooling everyo

You want to give each user a fixed amount of storage. But most users don't use anywhere near their total. So you oversubscribe to save money by pooling everyone's storage in one massive SAN. I imagine Gmail does something similar. I bet if every Gmail user suddenly started using 100% of their email storage Google couldn't cope. But Google knows this won't happen. Over subscription is how you make money in the end. Getting better at figuring out exactly how much you need when you need it directly affects your margins.