There are a few good use cases for root shares, Space Invader One has a recent video on it:
Unraid & Moving Data (Part 4) RootShares
And also covered in this older video with lots of other useful tips and tricks with SMB shares:
Unraid Shares in Depth - PT1 Windows and SMB
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Thanks for the reply. Yes that was my first though, however permissions for most other folders and files in the share are being changed too, so harder to track down as have lots of container mapped to the whole array. I can at least narrow it down to container that have access to the share though.
There were a few containers without a PUID and PGID variable, so added those, but that didn't fix the problem. Think the next step is to look at umasks, I've ssh'd into each container and they've all running under 0022. Had some good advice in the unraid subreddit, sounds like changing umasks to 002 or 000 where supported might work?
Not sure if the permission changes are something that would show up in the logs? If so, any idea what I should be looking for?