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I have a 2 TB external USB drive partitioned into 3 "drives." Two are ~500 MB, the third ~1 GB. I have lots of spare space in the middle partition, so wanted to make it smaller and give that space to the third partition.

I was able to resize the middle partition smaller using Yosemite's Disk Utility. However, when I tried to enlarge the partition that was "last", i.e., the bottom of the partition diagram, to give it the now unallocated space, the sizing handle was at the bottom of the diagram and couldn't move down and I couldn't drag the start of the partition up in the diagram.

Can you only make a partition "longer" and not move the start or "head" of a partition? That's all I could think, but was unable to find any documentation on this. There is a box where you can enter a size value for the partition, but I was too chicken to try it without asking here first.

Thanks.

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  • Thanks, lkanomath, I may look into iPartition, though this is the first time in many years I've wanted to repartition, so buying a 3rd-party app may be overkill.
    – Bosque Bill
    Commented Feb 28, 2017 at 17:11

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In Disk Utility a 2 TB disk with three partitions (2x500 GB & 1x1 TB) looks like this:

enter image description here

In Terminal and using gpt you will get the following output:

sudo gpt -r show disk3
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34           6         
          40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      409640   976562504      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
   976972144      262144         
   977234288   976562504      3  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  1953796792      262144         
  1954058936  1952044320      4  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  3906103256      262151         
  3906365407          32         Sec GPT table
  3906365439           1         Sec GPT header

The partition with the index number 2 is Volume1, index number 3 is Volume2 and finally index number 4 is Volume3. The 262144-block areas of unallocated disk space are standard Apple partitioning policy.

After resizing the second partition to 250 GB Disk Utility shows the following:

enter image description here

and gpt ...

sudo gpt -r show disk3
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34           6         
          40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      409640   976562504      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
   976972144      262144         
   977234288   488281248      3  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  1465515536   488543400         
  1954058936  1952044320      4  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  3906103256      262151         
  3906365407          32         Sec GPT table
  3906365439           1         Sec GPT header

Expanding the fourth partition (Volume3) would require to move its first block (1954058936) to lower block numbers e.g. block 1465777680.

This can't be done with on-board tools like Disk Utility or command line tools like diskutil. 3rd party tools like iPartition or Stellar Partition Manager are capable of doing this though.

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