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I have two different 3TB SATA hard disks:

  • a Toshiba DT01ACA300
  • a Seagate ST3000DM001.

I also have access to two different USB 3 HDD docks:

  • a Connectland DOCK-CNL-YJK3519-V3+ES
  • a Focus SATA + IDE dock (exact model name unknown)

It turns out that if I partition a disk on the Connectland dock as GPT with one HFS+ volume, the disk would become unusable when I plug it onto the Focus dock; OS X Yosemite would complain that the disk cannot be read and suggest that I initialize it.

Same thing the other way around: if I partition a disk on the Focus dock, the disk would be unusable on the Connectland dock, and OS X Yosemite would complain that the disk cannot be read and suggest that I initialize it.

This happens to both Seagate and Toshiba disks.

In both cases, the disk would be recognized as a 3TB disk. I can also use the full capacity of the disk, provided that I put the disk on the dock where it was partitioned and formatted - i.e. if I partitioned and formatted a disk on the Connectland dock, I would have to keep using it on the Connectland dock.

What's going on? How is this even possible? How am I even supposed to shop for a new dock reliably if my dock dies?

  • If you format the disks with just a single HFS+ volume, does the same problem still exist? – Flying Trashcan Dec 16 '14 at 15:26
  • @FlyingTrashcan I was already formatting each disk as a single HFS+ volume, with GUID partition table, using Disk Utility. Do you mean there is some other way I should try to partition the disks? – Kal Dec 16 '14 at 15:34
  • Sorry, I misread your question. When I think of "partitioning" I think of splitting the volume into 2 or more partitions. You were already doing what I asked about. I wonder if you could format them in a computer (if you have access to a Mac Pro) and then try them in the docks. My guess is the docks are doing something weird with the formatting, but I have no idea how to fix them. – Flying Trashcan Dec 16 '14 at 15:40
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The problem will lie with the dock disk-controllers and the method they use when translating the hard disk layout. I recently serviced an HP NX7400 laptop and the BIOS has two different modes for dealing hard disk translation - LBA Assist and Bit-shift.

Both work, but if a drive is formatted using one method it will not be recognised if the other option is then selected after partitioning and formatting.

The acid test would be to format both disks, one on each dock, and then hook the drives up directly to a Mac. I suspect one of the drives will be recognised and accessible but the other will pop a "Disk Unreadable" message and prompt to be initialized.

  • Thanks for the info! I realize there are now USB-attached SCSI (UASP) docks. I'm pretty sure that my newish retina MacBook Pro with OS X Yosemite can support that over USB 3.0. I just chatted with a tech support representative from StarTech; they say that, with a UASP dock, LBA-assisted vs bit-shift will be a non issue, as the host will have lower level access using SCSI commands sent over USB. They say that UASP docks will also not impose a capacity limit, for the same reason - any capacity limit will be the host's problem, not the dock's. Would you vouch for that? – Kal Dec 17 '14 at 14:15

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