External disk - Unrecognized file system (-69846)
Try this in the exact order:

#FOR THE WHOLE DISK
diskutil eject /dev/disk2               #Eject the disk 
diskutil mountDisk /dev/disk2           #Re-mount the disk

#FOR THE VOLUME(S) OF THE DISK
diskutil list                           #list volume identifiers. 
diskutil mount /dev/disk2sXXX           #Mount the Volume. Dont enter a disk ID
diskutil repairVolume /dev/disk2sXXX    #Repair the Volume. Dont enter a disk ID


Basically you are trying to correct previous mounting/ejection related errors by making sure the disk is safely ejected before you do anything else. 

Once that is out of the way, have the disk re-mounted. Next, have the volume re-mounted. Finally, repair the newly mounted volume.

Additionally, double check for any human error. Did you want to repair the volume or the disk because you specified a disk identifier to repair a volume. You typed:

diskutil repairVolume /dev/disk2 

it should be

diskutil repairVolume /dev/disk2sXXX

Or use repairDisk if you wanted to repair a disk.