Target disk mode very slow in one direction

This is purely a guess, but I think when the MBP boots into target disk mode, it's not actually running Sierra.

Therefore, I think Sierra updated the firmware and broke TDM over TB.

For my MBP, the latest firmware version I can find a reference to online is: MBP112.0138.B16

But my MBP is showing: MBP112.0138.B18

I tried rolling the FW back to MBP112.0138.B16 using:

sudo /usr/sbin/bless -mount / -firmware ~/Downloads/MBP112_0138_B16_LOCKED.scap --verbose

But it returns with an error:

Could not set boot properties: 0xe00002bc

Error while writing firmware updater for EFI

The Thunderbolt driver is version: 17.1

I did some Blackmagicdesign tests as well.

MBP (Retina, 15-inch, Mid 2014) with Sierra in TDM connected to an iMac: Write 8.6MB/s, Read 7.2MB/s

MBP with Sierra using IP over TB to iMac: Write 89.6 MB/s, Read 20.1 MB/s

A different MPB, same specs but with El Capitan in TDM connected to iMac: Write 668.7 MB/s, Read 448.6 MB/s

It appears that Sierra 10.12.3 improves this issue but I don't think that it is fully solved yet.

I'm now getting ~340-345MB/s read/write on Target Disk Mode, but I'm pretty sure that I used to get closer to ~650-700MB/s. So that is still only around half the speed that it should be capable of. However, if I boot up into Sierra and use the Thunderbolt bridge, then my numbers jump up to ~590 MB/s write and over 800-900MB/s reads!

Here is a snapshot of the test while using Target Disk Mode:

Note that the Boot ROM Version reported by System Information is MBP112.0138.B21.

I am also seeing terribly slow speeds accessing a mid-2014 MacBook Pro in Target Disk Mode over Thunderbolt that has been upgraded to Sierra.

The Blackmagicdesign Disk Speed Test is reporting an average of ~9.7MB/s write and ~11.3MB/s read rates of the MacBook Pro drive from both a 2013 iMac and a 2015 Retina iMac. By comparison, if I boot the MacBook Pro up and connect using an "IP over Thunderbolt" bridge, and then run the test from an iMac to the notebook drive, I get between ~73-123MB/s write and ~59-121MB/s read rates depending on the number of times I run the test.

While something appears to be very wrong with Target Disk Mode over Thunderbolt from the MacBook Pro, even the Thunderbolt bridge was slower than I had expected. I regularly use Thunderbolt bridge shares between my iMacs, while I don't get the full speed of the SSDs over the bridge, I do usually get closer to 380MB/s writes and over 500MB/s reads. The MacBook Pro is not keeping up with even those numbers, even though the MacBook Pro is getting ~642MB/s writes and ~726MB/s reads against its own drive.

I also ran the test from the MacBook Pro against the main SSD on the Retina iMac, and got ~105MB/s writes and ~95.6MB/s reads. At this point, it looks like something is wrong with the Thunderbolt speed on the MacBook Pro.

I wholly agree with your assessment that the firmware has been updated and agree that Sierra is not running when in TDM. I checked the system information for the affected MacBook Pro and found that it is also running "Boot ROM Version: MBP112.0138.B18". I've submitted a bug to https://bugreport.apple.com/. According to the accepted answer on http://stackoverflow.com/questions/144873/can-i-browse-other-peoples-apple-bug-r eports , we should probably each submit the bug in order to help gain visibility to this issue.

Well, I tried to downgrade the firmware with no success. I used a Mavericks installation at first and did not get the error that you did, but the downgrade never occurred. I then tried it from Sierra, and got the same error message that you did. At this point, I guess I will just wait to see what Apple comes back with. I'm going to go try to see if the ethernet or usb ports on my Belkin Thunderbolt Express Dock is running slow with this machine too. If so, then yikes!

Adding "--recovery" got rid of the error for me. But the FW is still at the same the same after a reboot.

sudo /usr/sbin/bless -mount / -firmware ~/Downloads/MBP112_0138_B16_LOCKED.scap --verbose --recovery

I've got an older iMac and MacBookPro (both 10.11.6) and looks a lot like I've been bitten by the same problem--Target Disk mode suddenly became truly glacial in the past few weeks and probably after one of the security updates. I'd like to hold off on Sierra if possible--anybody got any workarounds for El Capitan users?

I have this issue too.

I have a lot of old macs so just the other day I did this connection succesfully from an iMac G3 400 Mhz to a G4 MDD; all went very smoothly.

Now I'm just connecting my Mini with the latest version of High Sierra to my MacPro running 10.7 and this is an extremely unresponsive party I must say.

The whole point with the Target Mode thing should be that it makes it easy for us to pick and choose files to / from our ancient macs. So it's really not helpful that a newer OS slows it all down to the "growing fingernail" status as someone so cleverly put it.

I know one of the disks in the MacPro has issues but this shouldn't slow down the entire machine, should it? It's not the boot disk.

In fact I am even communicating SSD to SSD here which really should be fast but... this is so slow, my heart rate goes up.

I can reply to my own posting here; after I had ejected (by dragging to trash / eject icon) the slow and faulty disk in the MacPro - which weren't even involved here I thought - it's all moving faster and not like the "growing fingernail" but rather in a more usual way. Phew!

I just found this: https://github.com/gdbinit/firmware_vault/tree/master/EFI/MacBookPro

Apparently B18 really did arrive with Sierra 10.12.2.

Did you upgrade one of your Macs to Sierra?

I'm having the same problem, except it's in both directions.

I like to boot my iMac5k from my MacBookPro's SSD using target disk mode. After upgrading the MacBook from El Capitan to Sierra 10.12.2, the boot progress bar on the iMac moves very very slow, like a fingernail growing. Once it reached 100%, after about 15 minutes, it simply hung.

Thinking it might have been an incompatibility issue between the iMac's El Capitan and the MacBook's Sierra, I upgraded the iMac to Sierra as well. The slow/non-boot issue remains though.

So I booted the iMac from it's own SSD and accessed the MacBook as a simple external drive. Transferring 3.5 GB in either direction takes about 15 minutes, which is about 5 MBs throughput. A far cry from the theoretical 20 GBs throughput advertised for Thunderbolt 2.

I suppose the slow throughput is happening in both directions for me because both Macs have Sierra 10.12.2 installed.

-Michael

Ross, can you check your Boot ROM Version on your MacBook Pro?

Thanks for the information GNXClone! I'm going to see if I can get the firmware downgraded. I'll let you know what I find.