A second side effect being that all drives disappear from my disk defragmter software (MyDefrag) & the entire drive becomes unusable for anything except UrRbackup’s temp directory. it’s rather frustrating as there’s only limited space on the OS drive. I’m running under Windows 2012 R2
This wasn’t an issue prior to upgrading to 2.2.11 but now I’m being plagued with low disk space warnings about that drive.
A partial workaround seems to be using windows to set a usage quota on that drive limiting usage to something under 90% of the drive - that at least gets rid of the annoying pop-ups from the system tray.
The event log still gets populated with low space warnings, however I can live with that. Sadly low space warnings in Windows can only be turned off globally (all drives) and the 10% space trigger is apparently hard-coded.
Do you have temporary file buffers activated in the advanced settings? If yes, this is kind of the expected behaviour if the temporary storage is not large enough…
Yes, presumably that’s the default as I don’t remember changing it, what would be the expected result of deactivating it? In terms of performance? Now I’ve killed the pop-ups, the event log I’m less concerned about, it doesn’t interfere the way pop-up notifications do… 
It’s explained here: https://www.urbackup.org/administration_manual.html#x1-700008.5.1 and is disabled by default nowadays.
Thanks, I may have enabled it some while back, as I when I first installed and read the manual I was using USB 2.0 storage, since the target for storage is now USB 3.1 I shall try without 