Unable to create webdav repo on my Synology NAS

I cannot get Kopia to work, which is almost certainly not because of Kopia, but because of me or the setup I am trying to accomplish.

I have a Synology 1815+ that I want to use as a backup server. Nothing more and nothing less. On the Syno, I run the WebDAV server app. I have a VPS in the cloud that I want to back up. This VPS runs Nginx Proxy Manger in a docker container. Kopia accesses the Syno WebDAV server via the proxy manager and a port forward on my router.

Both Rclone and Kopia access the WebDAV server, but not without problems. Rclone commands sometimes fail on the first attempt with an error like this:

2023/01/17 09:42:32 Failed to create file system for "remote:path": read metadata failed: 424 Failed Dependency

More often than not, it succeeds on the second attempt. Kopia fails 100% of the times when I try to create a webdav archive. It initially seems to start well, but fails after what seems like forever, with errors like:

ERROR error populating repository: error flushing writer: error flushing manifests: unable to write content: unable to create pending pack: unable to get session ID: unable to write session marker: unable to write session marker: s51659e833010f20dc62c028e98099b99-s5e9c22c903adf73b118: unable to complete PutBlob(s51659e833010f20dc62c028e98099b99-s5e9c22c903adf73b118) despite 10 retries: unable to complete WriteTemporaryFileAndCreateParentDirs despite 10 retries: Write s/516/59e833010f20dc62c028e98099b99-s5e9c22c903adf73b118.f-1976235410884491574: 500

The destination folder on the Syno then contains a sub folder and a few files:


The strange thing is that I managed to create a repository once. In that case, the first attempt failed, but the second succeeded. I even made a first test backup. Since I then decided to choose a different RAID type, I re-initialised the Syno storage pool/volume. From then on, I can’t get Kopia to work. Did Kopia leave things behind after that initial, successful repo and backup creation, which now interferes with creating a new repository?

I think it has to do with an unreliable connection, but I’m no expert in this field (understatement) and don’t know how to figure out where to look and waht to look for. I can’t imagine it’s my1Gb/s fibre connection. So is it poor performance of the VPS and/or the proxy manager used? Or is it poor performance of the Syno, which is not that fast, I have to admit?

Is there anyone who recognises these kinds of problems and/or has suggestions on how to investigate and solve them? Or is that a hopeless endeavour?

Thanx in advance.