Since I just installed a NAS, and I want to transfer several TB from my Mac Pro's internal hard disks (4 of them), I wanted to make it faster by connecting those hard disks directly to the NAS using an USB 3 Dock that I have a use regularly.

However, that doesn't work:

1- All my hard disks (internal as well as external used in the docks) are formatted with Disk Utility with a single HFS+ journalized partition

2- The Dock works quite fine with hard disks that have been partitioned and used from the Dock itself, both when connected to the Mac Pro or the NAS. I can transfer data like that, by doing two copies (which actually doesn't save time because there are 2 transferts instead of one).

3- Obviously the internal hard disks work quite fine when inside the Mac Pro. No issues found with First Aid or SMART for example.

4- Internal hard disks are unreadable when installed in the Dock: they do not show up in the NAS, and the Mac asks to initialize them (which I don't of course).

5- Dock hard disks are unreadable when installed internally in the Mac Pro, who asks to initialize them (which I don't of course).

So I suspect the Mac partitions or formats the hard disks differently when it's an internal hard disk vs when it's a hard disk inside some enclosure or dock.

How can I find out? Is there a way (forward looking) to format the hard disks in such a way that work both internally and installed internally in the Mac Pro.

Note that I now run Mac OS X El Capitan, but this is not a new issue. I remember having seen the same problem a rather long time ago in a different context (when upgrading an internal hard disk to a larger capacity one).


  • do you use FileVault? – Gabkano Dec 3 '15 at 10:15
  • no, I don't use FileVault – Jean-Denis Muys Dec 3 '15 at 12:12
  • A wild guess - that one is bitshift, the other is LBA-shift -dewassoc.com/kbase/hard_drives/… I've heard of this happening on other external dock scenarios - though I don't know a thing about it other than it was once found to be the answer. I'm planting this link here in case someone smarter than me knows what to do with it. – Tetsujin Dec 3 '15 at 14:45
  • quite puzzling. My gut feeling is that this explanation is unlikely. BT the document you link to has last been updated in 2003. All hardware mentioned here is newer by many years – Jean-Denis Muys Dec 3 '15 at 15:11

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