I was backing up some data to a DMG (sparse bundle) that’s stored on my NAS, when the power went out. It’s since been restored, and now when I attempt to mount the dmg, it fails. I’ve tried to “Verify” and “Scan Image for Restore” using Disk Utility, but I receive the error’, “Resource Temporarily Unavailable.”
Any thought or suggestions as to how to recover this DMG, and make it mountable again?
My guess is you’ll have to start over.
I really hope not, as the damned back up has been running for 3 weeks, backing up 4TB of photos from my RAID to my NAS.
This very situation has been tagged as a good reason not to use a NAS for your Photos library. I realize you’re not doing exactly that but the situation is similar.
Does that sound right? I don’t have a RAID or a NAS but Carbon Copy Cloner does an initial cloned backup of that amount of data in a few hours and incremental backups usually in 30 minutes. (I also have CCC perform a monthly ‘Find and Replace Corrupted Files’ search during backup which takes about 6 hours total for that monthly backup operation.) And BackBlaze does continuous background backups too, with all new files usually backed up within the day. Three weeks?
Agree you will probably have to start over 
While 3 weeks doesn’t sound right, I can clone 2TB
Mac to NAS in 40 minutes, copying a 50GB Photo
Library file (from same Mac) to (same) NAS takes
4 hours! I have some guesses but can’t explain that.
While it doesn’t shed much actual light on @TallTrees’ particular problem, this article, from a source I consider extremely reliable, contains some interesting points about why backing up one’s Photos library is problematic. It shouldn’t be so, of course, and IMHO Apple needs to put some effort into improving this. I find it particularly annoying that Apple’s official stance is to use Time Machine, while at the same time they are making it difficult to do so.
I don’t think they have an official stance recommending Time Machine any more than they recommend using Pages or Calculator. (And I don’t use any of those.)
The article I linked says “Apple still recommends using Time Machine to back up Photos Libraries which are kept on internal storage.” I realize that the source isn’t authoritative but Hoakley’s material is, at least, highly regarded.
My point, though, was that Apple provides a backup solution that used to work with network drives (Time Capsule and its ilk), Apple no longer manufactures that line, and there doesn’t seem to be any network storage that reliably fills the void.
I was going to disagree but Time Capsule was a form of customized NAS, so point taken.
May I ask why you were backing up to a DMG instead of a folder?
And, FWIW, I had to deal with so many corrupted photos libraries (mine & my users) over the years I only backup the originals folder in the .photoslibrary file.
Hi all,
Sorry about the delayed response. I’ve been unavailable for a bit. Thanks for all your responses.
@WayneG - TimeMachine uses a Disk Image on NAS, and Chronosync actually recommend the same. Backing up to a Disk Image stored on NAS offers better performance and allows you to preserve all file metadata since the disk image is formatted with a macOS file system.
I’m not backing up .photolibrary files, at all. I’m backing up individual RAW, JPEG, TIFF and PSD images, sorted and stored in folder structures. I use Capture One as my digital asset manager referencing the stored images on my RAID, with the Catalogs stored on my internal drive. My catalogs are backed up to an external drive, multiple times a day, as well as to my CrashPlan account. I also run a bootable backup of my internal drive daily to an external drive, so the catalogs are backed up as well.
After rebooting my Mac again, I was able to mount the DMG. I’ve since run Disk Utility against it, as well as Disk Warrior, and all is working well.