Tracking down those missing bytes


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A reader of Storage magazine recently wrote to say he had purchased an Imation Odyssey with 80GB and 160GB cartridges (removable hard disk drives) to back up one of his computers. He was surprised to find several gigabytes of capacity missing. Then he spoke with a storage architect who told him he discovered only 41TB of storage space existed on a new enterprise array that was expected to deliver 45TB.

It's a common problem and one that prompts the question: Who took a byte, megabyte, gigabyte or terabyte out of my storage, and where did it go? Should I blame the disk vendors, or the server and software vendors?

There are two main reasons for the discrepancy between what's advertised and what you get. One has to do with rounding up numbers and the other with how the storage is configured.

Disk drive manufacturers use base 10 (decimal) to count bytes of data, while memory chip, server and operating system vendors typically use base 2 (binary) to count bytes of data. This can lead to confusion when comparing a disk drive base 10GB with a chip memory base 2GB of memory capacity, for example, 1,000,000,000 (109) bytes vs. 1,073,741,824 (230) bytes.

Moving forward, a new nomenclature based on the International System of Units will use MiB, GiB and TiB to denote million, billion and trillion bytes for base 2 numbering. For base 10 numbering, it

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will be MB, GB and TB, respectively.

This was first published in December 2007

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