Time machine slow and stops Recently I've a problem with TM, i do usually attach the HD every week, but lately it's not backing up and it's extremly slow.

In particular, If i start the backup it says something like: backin up 21GB taking 10 hours . Which is way too much.

Moreover, I left the pc on (using caffeine) the whole night and this morning no backups were made. But TM is set up to take backups every hour. If I start it manually it runs for a while and then suddently stops. Saying nothing.

Any thought on how i can investigate the problem and solve it?

EDIT
Apparently there's a file/folder that makes the problem
. It's been stuck at the same amount 15,6 GB for 1hour without moving. I think the problem is there. any way that I can know what's going on?
A few hunches based on non-TM file transfer errors I've seen on macOS:


I would use Disk Utility to scan the drive and repair errors. https://support.apple.com/kb/PH22243?locale=en_US (Usually I tell people to back up any critical data first, but I assume you have a semi recent backup :))
Is the problematic folder a symlink to an external drive by chance? (Rare but something I've seen.)
How is the external attached? Check/swap cables &amp; ports if you have spares available.