Synology: Ensure cache dir is set on data partition

[techdaddies-kevin]

We had borgmatic set up on one of our Synologies, but I can't remember which method we set it up with. Long story short, Synology only provides VERY little space on /. Borg was running fine for months, but its cache was being written to /root/.borg (Or something like that) and so, a time came when / had no space available, so Synology stopped functioning correctly. We had to SSH in to figure out what was going on and to remove the cache. I haven't had a chance to reinvestigate yet, but if the setup instructions are indeed allowing Borg to write to /, they should be adjusted to cause Borg to write its cache to the shared folder location.

[m3nu]

This is true. I usually symlink the .cache folder to the main data folder due to that. If you have many files, this is a must.

Wanna do a PR to document this?

[techdaddies-kevin]

Yeah I can totally write up something later this week. Just to clarify - You only do this symlinking on Synology devices, right? On a standard linux machine, this isn't necessary, right?

[m3nu]

Yes, only on Syno because if you run the backup as root user, there is limited space in /root. So I link it to /volumexx/homes/root or something instead. It could be that /volume/homes/root gets copied during updates, but I'm not sure.

[markjorritsma]

I have run into this issue when setting up a 5TB backup.
The root partition of my DS415+ (DSM 7.1) is (only) 2.3 GB, with approx. 86% used before setting up.

Borg quickly filled up the remaining 14% with cache files, after which it stopped.
Fortunately I did not impair the rest of my NAS' functionality much, so I could remediate the issue.

I think the documentation for Synology should be updated with a section specifically for large backups to setup a cache dir on the disks (/volumeX) instead of /.

Using this discussion I was able to setup a symlink from the /root/.cache directory to /volume1/
Furthermore I excluded the /volume1/ in my borgmatic configuration so that it will not be included in the backup.

[m3nu]

Valid point. Maybe this can be set inside the Borgmatic config to have it all in one place.