Data recovery from 2012 MacBook Air SSD using 2011 MacBook Air Unfortunately my 2012 MacBook Air came off second best with a cup of coffee. Everything toasted except the SSD! As luck would have it, I have access to a 2011 MacBook Air (El Capitan) which I am now using. The only issue is I would like to get the data off the old one.

I have removed the SSD, purchased a SATA converter which I plug the SSD into, and then a SATA -> USB cable to plug this into the 2011 MacBook Air.

When I plug this in, the disk does not mount. From inside the OS I can 


See the SSD in Disk Utility however it won't let me mount (button disabled)
Run First Aid, which runs successfully with no issues


From single-user mode, I have tried the following


fsck /dev/disk2s2 - this says 'unknown volume signature : 0' and then gives a series of hex readouts
sudo fdisk /dev/disk2s2 - this results in 4 rows, all of which have zeroes in every column entry
Added as an answer after comments...

Initially a guess, that the disk was formatted APFS, which would be unreadable by El Capitan.

Upgrading to High Sierra would enable the disk to be read &amp; written as normal.

As regards permissions; you could either add yourself to the user list, as an ACL, or you could just Get Info on the drive itself &amp; check the 'Ignore ownership on this volume' box.