18TB Western Digital Red Pro NAS Hard Drive Expired

The entire size of your drive is detected properly. When hard drive manufacturers advertise the size of their drives, they use the "metric" meaning of mega, giga, and terabyte. To a hard drive manufacturer, 1 terabyte = 1,000,000,000,000 bytes (one trillion bytes). So an 18 TB hard drive is 18,000,000,000,000 bytes of storage space to a hard drive manufacturer.

Depending on the software you are using, it may use original "binary" definition of megabyte, gigabyte, and terabyte. 1 kilobyte was defined by software programmers as 2^10 bytes (2 to the tenth power). This is 1,024 bytes. Close to a thousand, but a little bit over. So to software programmers and purists, 1 kilobyte is not 1000 bytes (metric definition), 1 kilobyte is actually 1024 bytes. That 24 byte difference explains why you are seeing 16.4TB in software while the drive manufacturer says it is 18TB. This 24 byte difference is magnified by the enormous sizes of modern drives.

Scaling this 24 byte difference up to a terabyte, the SOFTWARE definition of 1 terabyte = 1,099,511,627,776 bytes.

Hard drive manufacturers want their drive sizes to impress customers, So they use the more favorable conversion. 18TB to a drive manufacturer means 18,000,000,000,000 bytes of space. They advertise an 18TB drive. And you get 18 trillion bytes of space. When software examines the drive's size, it will usually use the other definition. Divide 18,000,000,000,000 by 1,099,511,627,776 and you get the size of the drive reported by your software: 16.3709 TB of space, which it rounds to 16.4TB.

In short, your system is working properly and there is no "unused space" being reserved on the drive. It is just using a different definition of a terabyte than the drive manufacturer. You got all 18 trillion bytes you purchased and the system is indeed using all of them.

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This is a great deal. 3 years more warranty (5 total) and you don't have to deal with shucking it at only $23 more than all time low price...

edit: I missed that one time the elements version went down to $280 so this is $43 over all time low but the point stands. 3 years extra warranty and less e-waste is worth a non-zero amount of money. this is the cheapest I've seen a full warrantied 18tb go.