Performance of MacBook Air SSD Targeted from iMac
So I tried it out and wanted to share my findings. First off, the equipment I was using:


Early 2015 13" i7 MacBook Air, 8GB Ram, 500GB SSD
Late 2015 27" i7 iMac 5K Retina, 16GB Ram, 1TB SSD


I restarted the Air in target disk mode &amp; plugged it into the iMac via Thunderbolt 2. It wouldn't boot. After a few minute, it just showed a ban icon (circle with a line through it).

I ran some 5GB Blackmagic Speed Tests to gather transfer rates (in MB/S):


iMac against its SSD - 1817 Read, 1510 Write
Air against its SSD - 300 Read, 241 Write
iMac &amp; Air against USB3 Flash Drive - 245 Read, 185 Write
iMac &amp; Air against USB3 External Drive - 160 Read, 170 Write
iMac using Air via Thunderbolt 2 shared folder - 400 Read, 490 Write
iMac using Air in target disk mode - 79 Read, 107 Write


So obviously there's a big performance loss for target disk mode.

If you're wondering why I'd want to target the air, it's because I mainly work off my Air and don't want the hassle of an external drive, thumb drive, file syncing, etc. I love the idea of getting to my office and "docking into" a faster processor, more RAM, and a big screen.