What happens when cloud storage runs out of space?

Cloud storage for my backups is filled to 99,6% and pops up a message “… you cannot update or synchronize files any longer” (Telekom Magenta Cloud).
So far however I didn’t notice any errors or warnings in the backup logs.
And I do see block files recently pushed into the cloud’s recycle bin, which indicates to me that backups still work normally.
This may be expected, since I’m not at 100% sharp yet, but I would like to know in advance how Duplicati behaves, once the cloud eventually refuses to accept or modify any more data.
Would I see a prominent error message, or somehwere hidden in one of the logs?

I already reduced retention periods, but due to recent additions, this may not help until a few weeks from now, so I will need to consider extending my storage space eventually.
Anyway, I’m curious to know what happens if I run out of space.

What Destination Storage Type are you using? Some can check space, some can’t.
In a log file Complete log, do you have some numbers about quota such as these:

      "TotalQuotaSpace": 999618043904,
      "FreeQuotaSpace": 79522951168,
      "AssignedQuotaSpace": -1,
      "ReportedQuotaError": false,
      "ReportedQuotaWarning": false,

You can see from last two lines that a quota aware cloud should be warning well in advance.

A failed upload should cause a big error message. Recovery difficulty can vary. Best not to fill.

quota-size

This value can be used to set a known upper limit on the amount of space a backend has. If the backend reports the size itself, this value is ignored.

can probably get you an early warning if your storage is not reporting, but first check your logs.

Essentially, uploads will fail, meaning that the backups will fail.

Other than this, you should see no ill effects. Since the delete process is (usually) run after the backup, you will not get out of the situation without performing a manual delete of some version.

Deleting a version is not supported with a UI operation, so you need to play around with the commandline (also wrapped in the UI) to remove a specific version.

which won’t by itself free much storage, but eventually now-wasted space will trigger compact.

Compacting files at the backend
The COMPACT command

Old data is not deleted immediately as in most cases only small parts of a dblock file are old data.

Compact uploads the new files before deleting the old ones, so needs some free space to do it.

It is entirely possible that the version delete frees up the storage of a dlist file, which is not large compared to the free space compact needs. Compact may run out of space trying to free space.

Out of space is an uncomfortable place to be, so it would be best if you can get the warnings up.

Some providers may count the recycle bin as space in use. It might be an easy way to free space. Testing by you would be needed.

do I need to set a specific option to get a complete log ? I usually have a log file written of “log-file-log-level = retry”.

they definitely do. Therefore I frequenty check and empty the recycle bin, but since only the minority there usuallly are dblock files (and the rest index and list files), deleting them doesn’t get me much space.

No. Just look in your job log. It’s the last line. Click it to open.

This makes no sense. There should be exactly one dindex per dblock, to index that file.