On my mac I have Time Machine configured to backup to a Sparse Disk Image Bundle that is located on my Raspberry pi, which it connects to over SMB and mounts on boot. As long as the mac is awake there is no problem at all to backup or retrieve files.
However, the problem occurs during sleep when Time Machine tries to backup during Power Nap. Once it wakes from sleep it displays the error message that TM backup failed and in the console I can find the somewhat more detailed message: "No destination resolvable"
To me it seems that during sleep the system dismounts all mounted volumes because it loses ethernet access at the point when it goes to sleep, but once it briefly wakes during Power Nap it does not remount the volume from the SMB share, but rather just looks for the previously mounted Sparse Disk Image Bundle at /Volumes/MyBackup/.
Once the system wakes fully from sleep it remounts the disk image without any problems.
So my questions is: is it possible to have the mac remount the Sparse Disk Image Bundle that is located on an SMB share to backup during Power Nap?
Best Answer
No - Power Nap is extremely selective about what activities it will take on and thus far, no third party hooks or API is provided by Apple to allow someone to easily modify what happens when the OS wakes from a nap.
Clearly, someone could reverse engineer things and come along with a solution, but that hasn't happened yet. If they do, we can surely come with a better answer but at the moment you get the behavior out of the box which isn't going to accomplish what you ask.