iMac (2013, Big Sur) Time Machine not accessing backup on Synology NAS

Updating this thread in case anyone has more info (or to help someone in the future learn from my mistakes). I’ve gone through about 10 separate attempts to restore my iMac from the Synology NAS Time Machine backup. Unfortunately after around a day or so each time, the process just freezes up after transferring *nearly* all the raw data. The computer is still interactable and the process can be cancelled, but the Migration Assistant window is always stuck on the “transferring files” screen without any files being transferred (after hundreds of thousands of files were successfully transferred).

I went and bought a 4TB external drive to attempt to copy over the backup bundle file from my NAS to the external drive and restore from the external drive instead directly. First attempt I had the external drive formatted as APFS (my mistake), and it wasn’t recognized properly while doing a first-boot system restore via freshly-installed OS Big Sur. I’ve now reformatted the external drive as MacOS Extended Journaled with the GUID Partition Map after reading this is Time Machine’s preffered drive format. I’m now transferring the backup bundle file (it’s 3.5TB…) and will attempt a restore when possible.

What I’m worried about though, on most of the guides I’m seeing regarding attempting to transfer a backup like this, it’s actually a folder I’m supposed to be seeing called “backups.backupsdb”. There is no such folder when interacting with the bundle file I see on my NAS.

I’m a bit at a loss, as it’s looking like I could be losing nearly a decade of data here if I can’t square this one way or another. It seems so ironic I got a NAS for the very purpose of having redundant storage for a foolproof backup solution, and now I can’t seem to even restore said backup now that it’s needed. 🙃

Thank you for the response. Migration assistant was the utility I was looking for.

Sadly I’m currently unsuccessful with my restoration efforts. Migration assistant discovers the NAS and the backup, and starts the process, but on all recent attempts (now I’m on attempt four) at some point the NAS ceases to transfer data. At first I thought it was due to attempting this over wifi, but even through Ethernet the longest it has lasted is about a day and a half before the NAS stops transferring. This leaves the “Transferring Your Information” screen on the Migration Assistant utility essentially frozen.

An additional issue that is compounding with this, every time I cancel a failed attempt, the computer seems to be holding on to whatever data did get transferred but in a difficult to access (hidden?) volume. A disk utility partitioning erasure combined with a fresh install of Big Sur seems to get everything back to stock. But this adds another hour on to every subsequent attempt.

For context the backup restoration is about 2.5TB, and even after de-selecting large categories like photos and videos from the restoration drop-down options, the process still fails. Every time this starts it claims a time estimate of 61 hours and 5 minutes. Transfer speeds tend to stabilize around 25-30MB/s over Ethernet.

Any thoughts? Would I have an easier time if I could somehow transfer the Time Machine backup volume to an decent external hard-disk drive (my largest external SSD is sadly only 2TB) and do this over USB? I have a sneaking suspicion this has something to do with the NAS itself not allowing for extended uninterrupted read times, or some kind of network issue.

I see, that makes a bit more sense.

Currently I’m still at a bit of an impasse. When I boot into recovery mode, I’m able to see the Time Machine backups on my new external disk (that is now formatted to the MacOS Extended Journaled format). Upon trying to restore the most recent backup from it (from the “Macintosh HD - Data on iMac” directory, October 2024, MacOS 11.4), it claims Migration Assistant is necessary. Yet when I open up the “Macintosh HD on iMac” directory the most recent backup is from July 2021, MacOS 10.15.7. The backups from this directory are able to restore to the current computer within recovery mode.

When I boot the computer up for the first time and have it run setup assistant, the backups on the external hard drive are not loading in/selectable. The drive itself is recognized in Migration Assistant as an iMac rather than an external drive, which is doubly odd. This is all with a clean install of Big Sur on a freshly-wiped 4TB internal SSD. The file formatting is APFS for the SSD, I don’t know if changing it to Mac OS Extended Journaled will change anything. I am not sure what the file formatting is for the drives in my NAS, but am sure the external new hard drive is the Extended Journaled format.

Any thoughts what might be going on? I’m going to attempt a restore from the 10.15.7 backup and see if after *that* be able to restore data from the 11.4 backup. This is so odd.

Another update, as I reach my wit’s end with this. Attempting the backup within the Time Machine Restore option (the 2021 10.15.7 backup) is also resulting in a hang. Over the course of ~6 hours it got to transferring/restoring 1.36TB, the same it would transfer when attempting this over the NAS with the more recent backup. But last night the progress completely stopped again and has shown no progress into today.

Oddly the iMac’s fans spin up and down periodically like it’s trying to do something, but this is leading me to wonder what’s really going on here. I’ll leave the system be for another day but I doubt any further progress will be made.

Another quick update. Still no full success.

-After reformatting the internal SSD to Extended Journaled I can do the migration assistant transferring every category *except* the 1.5TB of photos from my library. Any attempt that includes the photos fails at exactly the same spot.

-Migration assistant won’t recognize the copied backup bundle on my external drive. It will in recovery mode but won’t allow me to do a restore, claiming I need to install OSX despite a clean install already there.

-Apple Support isn’t quite sure either what’s going on here. I’ve got an appointment at an Apple Store soon, hopefully they can take a look at verifying if the backup bundle on my external drive is corrupted. I have no real way of having them assess the NAS original bundle.

As this process drags on it seems I’m about to lose over a decade of freelance photography files. 🙃 Won’t be trusting Time Machine for stuff like this ever again. Doing file storage the manual way on my NAS with redundancy seems to be the only way forward from here.