Not enough free space – but there is

[Alcuin]

Sonarr version (exact version): 3.0.6.1342
Mono version (if Sonarr is not running on Windows): 6.12.0.122
OS: macOS 12.2.1 Monterey (running on a Mac mini with Apple Silicon M1 chip)
Debug logs: https://pastebin.com/FiAjHfC6
Description of issue:

I have lots of downloaded (via sabnzbd) episodes that don’t get moved from the sabnzbd Downloads folder to the TV shows’ destination folder. This destination folder (TV Shows) is located on my Synology NAS within the mounted volume /Volumes/videosyno2 on the Mac mini. The System > Events (Sonarr GUI) list shows that the component FreeSpaceSpecification reports “Not enough free space (414 998 528) to import …”.
The output of the df command shows that this volume has 8 TB free.

Filesystem                                         Size   Used  Avail Capacity     iused      ifree %iused  Mounted on
//admin@DiskStation._smb._tcp.local/videosyno2     27Ti   19Ti  8.0Ti    71% 20209916710 8590338808   70%   /Volumes/videosyno2

Sonarr, however, only sees <400MB on this volume:

I found a few questions here but none had a final solution post or was specifically for my kind of setup/machines.

I read that this might be a problem with permissions – but what can I check, where can I start to look into?
Moving via sabnzbd downloaded episodes worked fine up til now, so there doesn’t seem to be a general problem with file/folder permissions. For me it looks like a bug that this FreeSpaceSpecification component incorrectly reports the free space?

[bakerboy448]

Sonarr does not have access on the mount to more than 394.7 MB of space it would appear.

[Alcuin]

Okay – but why? The OS does have the access. Is it a Mono problem, maybe?

[Alcuin]

Interestingly enough, Radarr does see the available free space correctly!

On the NAS side, both folders (TV Shows and Movies) inside the shared folder videosyno2 have the exact same permissions (RWXRWXRWX), ownerships (admin) and group memberships (users).

[Alcuin]

Another observation: when Sonarr is in this state (not being able to move downloaded episodes to the destination folder because of insufficient disk space there (apparently)) it crashes a lot. It seems that it crashes every time it tries again to move a file.

[Alcuin]

Now THIS is fun: I manually moved a few files (a few GB) to see what free space Sonarr would report after those apparent 394.7 MB. Will it be a negative number? To my surprise: no! Look at this now:

Still wrong (because the correct number would be around 8 TB. BUT now the move process can continue (for the next 4 TB, at least).

So, looks definitely like a bug to me.

[bakerboy448]

Presumably will go away with the eventual switch to dotnet

[Alcuin]

Just another info: the Sonarr update to version 3.0.7.1477 didn’t fix this problem.