I am trying to recover about 162 GB of drive space by deleting device backups from ~/Library/Application Support/MobileSync/Backup on a MBP running El Capitan (10.11.6.) To be safe I dragged the Backup folder to a folder I created on a NAS, thinking this would simply copy the folder and its contents over. Instead the folder disappeared from the local drive and was nowhere to be found on the NAS.
I think I understand why the drag operation failed without warning*. But the problem I face now is that I have no way to reference the Backup folder in order to actually delete it. Thus 162 GB are occupied with apparently no way for me to free them up. With about 2 GB of free space on that system drive the machine is crawling.
Any thoughts on how I might free up that space without reformatting the drive would be much appreciated.
*This NAS holds Time Machine backups of two MPBs, as well as a couple of shares used for temporary backup storage. If memory serves, rather than mounting the share properly, and accessing it in Finder from the Shared or Devices section of the sidebar to set the drag destination, I created a folder, possibly inside the folder containing the TM backup, and used that as the drag destination. The "copy" was instantaneous (a dead giveaway that something was wrong), and then I later could not find the folder I had created, nor the Backup folder I had copied. Dumb mistake, likely due to sleep deprivation, or lame human multitasking.