[michelh]

Thanks for your reply. I did as you suggested. Subsequently I used SD to backup the computer to an external HD and to a sparse image on a Synology NAS drive. The backup worked for both, but the sparse image did not unmount with the message that the disk is in use and cannot be ejected. The only way to unmount the sparse image and NAS drive was to restart the Mac.

This unmounting problem only happens when using SD. There are no problems in normal use of files on the NAS drive or in opening the sparse images on the NAS drive. I am not sure if this is only a problem occurring in backing up the computer. I use SD with other volumes without issue but then these are less than 5GB.

The Synology wiki community could not give any suggestions if the NAS drive is at fault. There are threads in the Apple discussion forums highlighting problems with Mac disconnecting external servers but no solutions seemed to have been found and Apple is being blamed.

Could you advise further please? Would using sparse bundles be better?