quota support, probably. Problem is, because a NAS is multi protocol filesystems, we have both CIFS (NT) and NFS. So UIDs/GIDs are a risky thing to go by.
I was looking at du and sums, which is almost what this script does. (A find and add, and the sum rather than a du. Don't know what this does to 'expense' of the process.)
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It's not pessimism if there is a worse option, it's not paranoia when they are and it's not cynicism when you're right.