Coincidentally I have noticed that the disk capacity reports in "About this Mac" and the Terminal when running diskutil list both report inconsistent capacities for an external hard disk drive.

This is an 2TB external hard drive. However, when adding the capacities of all partitions I get a value which is significantly below:

0.2+885.2+0.1+400.0+0.1+300.0+0.1+49.5=1635.2 (GB)

How is this possible? Where did the remaining ~365GB go?

This disk had been formatted and used under OSX Mountain Lion.

   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *2.0 TB     disk2
   1:                        EFI                         209.7 MB   disk2s1
   2:          Apple_CoreStorage                         885.2 GB   disk2s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk2s3
   4:          Apple_CoreStorage                         400.0 GB   disk2s4
   5:                 Apple_Boot Boot OS X               134.2 MB   disk2s5
   6:          Apple_CoreStorage                         300.0 GB   disk2s6
   7:                 Apple_Boot Boot OS X               134.2 MB   disk2s7
   8:       Microsoft Basic Data EXCHANGE                49.5 GB    disk2s8
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Time Machine           *299.7 GB   disk3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Media                  *884.8 GB   disk4
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Time Machine 2         *399.7 GB   disk5

Unformatted space.

eg, I have a 500Gb disk with just a 27Gb partition:

   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *500.1 GB   disk0
   1:                       0xBF                         26.8 GB    disk0s1

You can confirm this in Disk Utility or a tool like iPartition.

In Disk Utility click on the drive itself, not a partition of it. Then, under the partitions tab you should see each partition, and then the greyed out freespace available on the drive. You can select it and it'll show you how much you have.

  • I think you're right. This is weird. I had formatted this disk freshly and left no free space on it. But later I resized an encrypted partition (name: Time Machine 2). For some reason this broke the partition table and caused inconsistencies in the available capacities. Now Disk Utility show unformatted space on the disk: link to picture – gentmatt Mar 19 '13 at 9:03

Very interestingly many applications display different base units. For example, Windows (as well as iPartition and other applications), by default display base-2 units. Mac OS X (Disk Utility, diskutil, etc) usually defaults to base-10 kilobyte megabyte and terrabyte units rather than using base-2 versions. That is, it will use KB10 rather than KB (or kb rather than KiB if using IEC unit names).

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