Drive data used discrepancy

I’ve got a quick question that I bet there is an easy answer for.

I have a 4-bay Drobo, according to Drobo dashboard it has 1.90TB of used space. I recently bought a 2TB external drive to make a backup copy of the contents of my Drobo. However the contents of the drobo will not fit on the new drive. Although drobo dashboard lists 1.90TB of used space, the “get info” feature on OSX shows 2.12TB of used space.

Is there a reason the drobo dashboard’s reading is lower? The contents of the Drobo do seem to add up to OSX’s stated 2.12TB

Thanks in advance.

OS X (Snow Leopard and newer) uses SI units for measurements - 1 KB = 1000 bytes, 1 MB = 1000 KB, etc.
Drive manufacturers also use SI units for measurements.

Drobo uses a mix, depending. Where you see TiB, it’s binary measure (1KiB = 1024 bytes, 1MiB = 1024 KiB, etc), where you see TB, it’s up for grabs.

So likely your Drobo is using 1.90 TiB of storage, or 2,089,072,092,774 bytes, which is larger than the 2,000,000,000,000 bytes your 2 TB drive is advertised to store (actual capacity varies slightly by filesystem format, make, and model).

SI prefixes - TiB vs TB, etc

Makes sense to me, thanks for the quick reply.

roughly 2Tb advertised (i.e decimal) is 1.82Tb binary (i.e what most OS’s will report)

the newest mac OS report the binary sizes (ie a 2Tb drive shows as 2Tb - plug it into windows or linux and you get 1.82TB)

its the same number of bytes - its the “terra” bit which changes!