I am running a 2019 iMac. I have it connected to a WD external hard drive via USB. I have been using it to backup Time Machine since 2020. The external drive has nearly 2 Tb of space available. This past week I upgraded my OS. See screenshot. When the update was complete, I initiated a TM backup. It has been 'in progress' now for 24 hours and is still not complete. Any suggestions as to why?
[Edited by Moderator]
iMac (2017 – 2020)
I've seen similar reports on other sites after various macOS upgrades.
Some users have blamed Spotlight. The idea being that if Spotlight is forced to reindex the drive that slows everything down including Time Machine.
My guess is that the problem is Time Machine itself. In normal operation, Time Machine checks every hour to see what files have been modified and thus need backup. That number of files is probably relatively small for most users and the comparison occurs quickly. After an upgrade/update there is potentially a much larger group of files that have to be checked before the backup can even begin. I suspect that's the issue you're experiencing.
When I've had this happen subsequent backups have occurred quickly unless I made significant changes to the system (e.g. adding/deleting a large number of files).
Later in the afternoon the backup appears to have completed. I am still very puzzled at the length of time involved. That has never been the case before. Thx.
iMac Time Machine backup
