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Incorrect capacity of backup media


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I have a brand new 750GB USB3 hard drive, with no files on it, that I want to use for backup media. Get Info confirms the amount of free space on the drive. But when I create a new media set and point to that drive, Retrospect says that 100% of the drive's capacity is 697GB. I tried to change the 697 to 740, but it changed back into 697.

 

How can I make Retrospect use the full capacity of the drive?

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I think that the problem is the two different common definitions of GB, one being 109 bytes, and the other being 230 bytes (more properly GiB or gibibyte). Most likely, the HDD manufacturer is using GB, and Retrospect is using GiB, because 750 GB = 698 GiB. 1GB ~= 0.9313 GiB. OS X Get Info also uses the 109 bytes definition of GB.

 

So most likely there's nothing missing and Retrospect is using all the available space.

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Thanks, that makes sense. Though the label in Retrospect's GUI is GB not GiB.

Few people know about, and even fewer use, the binary prefixes (Ki, kibi- (210 = 1024); Mi, mebi- (220 = 10242); Gi, gibi- (230 = 10243); Ti, tebi- (240 = 10244); etc. It's not just Retrospect that's like this. Main memory sizes are almost always written as, say, 4 GB, when what is meant is 4 x 10243, and where it would be clearer to use 4 GiB.

 

Unfortunately, there is also a JDEC standard where K = 1024 (rather than k for 1000), M = 10242 and G = 10243. Just to help confuse things.

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