Add Synology DSM version 7 to the FAQs

[Silver-Saucepan]

Add instructions on how to configure Synology devices running DSM7 for use with SSH-mode BIT profiles

[aryoda]

@Silver-Saucepan Thanks a lot for your contribution!

Your PR is related to #1674 (where I wanted to write a FAQ entry too) and does save me a lot of time now :-)

Would it be possible to check if Synology's Audio Station shows a wrong "used disk" size for the backup folder (since it seems to follow the links too instead of ignoring them = effectivly overcounting the used disk size...)

[Silver-Saucepan]

@aryoda Yes, when Synology's File Station calculates the size of a folder it does not seem to be inode-number-aware, so each hard link within the folder is treated as a separate file, even if it links to a file who's size it has already counted, and so its size is added to the total. Thus the calculated size of a BIT snapshots folder can be many times its actual space usage on disk.

You might know this already but, the GNU du command does seem to be inode-number-aware and so can be used to get the actual space usage, counting additional hard links to a file it has already encountered as zero size. e.g. if the snapshots are in a folder called 1 then du -hs 1/ shows the actual space used. However, if you use du on an individual snapshot folder (e.g. du -hs 1/20240819-061501-243 it includes the size of 'files' that are actually hard-links to files in other snapshots.

This should probably be described in the DSM 7 section of the FAQs, and DSM 6 probably has the same behaviour but I can't test it to be sure.

[buhtz]

Would it be OK if I merge this?

[Silver-Saucepan]

It's OK by me. I tested it on a NAS running DSM 7.2.1

[buhtz]

It's OK by me. I tested it on a NAS running DSM 7.2.1

Thank you very much. This helps a lot.