UNC paths vs mapped drive letters
You can point a scan at a share two ways: a UNC path like \\server\share, or a drive letter you've already mapped to that share in Explorer. Both reach the same data, but a UNC path doesn't depend on the mapping still existing, which matters if you're scripting a scan or handing instructions to someone else — a mapped letter like Z:\ might point to something different, or nothing at all, on their machine.
If you're saving or scheduling a scan of the same share repeatedly, using the UNC path directly avoids the scan silently failing later because a drive mapping was removed or reassigned.
The account running the scan decides what it can read
A scan of a share only sees what the Windows account running it has permission to read. If you're logged in with a personal account that has limited access to a department share, the scan will report sizes for the folders you can open and simply skip or under-report the ones you can't — often without a loud error, just a smaller total than the share actually holds.
If the numbers look too small for a share you know is large, that's the first thing to check: run the scan under an account with broader read access to the share, rather than assuming the tool undercounted.
Why network scans take far longer than local ones
Scanning a local NTFS volume mostly reads metadata that's already cached or quick to fetch from the disk's own file table. Scanning over SMB means every directory listing and file attribute is a network round trip, and round-trip latency — not bandwidth — is usually what makes a share scan feel slow, especially over a VPN or a WAN link between offices. A share with millions of small files in deep folder structures is the worst case, because the number of round trips scales with the number of items, not their total size.
A gigabit LAN connection to a nearby file server will scan noticeably faster than the same share reached over a VPN to another site, even though the total data being reported is identical.
Scanning during off-hours
A full scan of a busy file server competes with everyone else's file activity for the same disk I/O and network bandwidth. Running large or recurring share scans outside business hours avoids adding scan load on top of a server that's already busy serving requests, and it also means the folder tree is more stable during the scan — fewer files being created or moved mid-scan means a cleaner, more comparable result.
Share permissions vs NTFS permissions
Windows applies two separate permission layers to a network folder: the share permission set on the share itself, and the NTFS permission set on the underlying folder and files. A scan needs to pass both. It's possible to have full share-level access but restricted NTFS permissions on a specific subfolder, which produces a scan that covers most of the share correctly but reports a handful of folders as empty, inaccessible, or missing entirely.
When a scan result on a share looks partial, checking NTFS permissions on the specific folders that came back empty is usually more productive than re-running the scan, since re-running it under the same account will hit the same restriction.
When this workload calls for a paid edition
A one-off look at a share to answer "why is this full" works fine with the free edition, run manually whenever you need it. Recurring server or share auditing is a different workload: scheduling a scan to run automatically overnight, exporting the result as a report you can compare month to month, and covering multiple shares from one console are all things the free edition isn't built for. That's the gap TreeSize Professional is positioned to fill, and it's worth reading the free vs Professional comparison before deciding which one your situation actually needs.
Network scan FAQs
Why does a network scan show a smaller total than the server's own disk usage report?
Most often because the account running the scan can't read every folder on the share. Check NTFS permissions on the folders that reported as empty or missing.
Should I scan a mapped drive letter or a UNC path?
Does scanning a share lock any files on it?
Will a VPN connection make a share scan unusably slow?
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