Disk & Storage Guide
By To scan an external drive for disk usage, connect it and pick its drive letter in the analyzer as you would C:. To scan a network drive, map the share to a letter or use its UNC path and point the tool's folder scan at it. Univik Disk Usage Reporter does this through Scan a Folder and exports an HTML or CSV report with full paths. Expect a share to scan far slower than a local disk, because each folder is a network request. Expect the result to cover only folders your account can read. WizTree's fast MFT scan does not apply to network drives. TreeSize Free scans shares but not in a commercial setting under its licence. For a quick total with nothing installed, PowerShell can sum a share.
The reason people scan an external or network drive is rarely curiosity. The 4 TB backup disk is full and the backup job is failing. The department share has hit its quota and three people are blaming each other. The NAS is at 95 percent and nobody remembers what is in the Archive folder. In every case the answer is a ranked list of folders with sizes, and the only question is how to get one from a drive that is not C:.
For an external drive there is no trick. For a share there are four things worth knowing before you start, and they are the difference between a scan that finishes over lunch and one that runs until tomorrow.
How Is Scanning an External Drive Different?
It is not, much. A USB hard drive or SSD gets a drive letter, Windows reads it through the same file system driver as an internal disk and a scanner treats it as one more drive on the home screen. Over USB 3 the throughput is close to an internal SATA drive, so the scan time is about the same, a minute or two per terabyte. Over USB 2, or through a cheap hub, it can be several times slower, which is worth knowing if a 4 TB archive drive seems to be taking forever.
Two small differences. If the external drive is formatted exFAT or FAT32, as many are out of the box, WizTree cannot use its NTFS file table shortcut and drops to a normal folder walk, though it still finishes. And an external drive that was used on a Mac may carry hidden .DS_Store and ._ files in every folder, which show up in a file type view as thousands of tiny entries. They are harmless and take no real space.
How Do I Scan an External or Network Drive for Disk Usage?
Five steps, the same for a USB drive and a share, with the network notes where they apply.
Connect the drive or map the share and check it opens
Plug in the external drive and confirm it shows under This PC with a letter. For a network location, either map it to a letter from This PC > Map network drive or note its UNC path, such as \\FS01\Projects. Open it in File Explorer first. If Explorer asks for credentials or shows Access denied, fix that before scanning, because a scanner running under your account sees exactly what you see and nothing more.
Pick the drive, or choose Scan a Folder for a share
Open Univik Disk Usage Reporter. An external drive appears on the home screen next to the internal ones with its free and used space, so click it. For a network share, click Scan a Folder and paste the mapped letter or the UNC path into the picker. Scanning one share at a time keeps the run short and the result readable. A whole NAS with a dozen shares is a dozen scans and a dozen reports.
Let the scan run, and expect the network to set the pace
A USB 3 external drive scans at roughly the same speed as an internal one, about a minute per terabyte. A network share is different: every folder listing is a round trip to the server, so a share with a million files can take a quarter of an hour over gigabit and longer over Wi-Fi. Scan from a wired PC close to the server, or from a machine on the same network as the NAS. The stop button ends the run early if you only wanted the top level.
Read the Folders view first, then Biggest Files
On a share the top-level folders usually map to departments, projects or people, so the Folders view sorted by size is the answer to who is using the space. Then Biggest Files lists the largest items with full UNC paths, which is what an admin needs to move a stray disk image or a forgotten video export. The File Types view shows whether the share is full of backups, media or mail archives.
Export the report before you disconnect
Click Export and save the HTML report and the CSV while the scan is on screen, because a network scan is the one you least want to repeat. Name the files after the server and share, for example FS01_Projects_2026-09-22.html. The disk usage report guide covers what to put in the report and how to print it to PDF for a ticket.
Why Are Network Drive Scans Slow?
A disk usage scan is a walk through every folder, asking each one what it contains. On a local drive that walk happens at disk speed, and on NTFS some tools skip it entirely by reading the file table in one pass. Over SMB, the protocol Windows uses for shares, every folder is a request sent to the server and a reply sent back, and the next request waits for the reply. The cost is latency multiplied by the number of folders, not bandwidth multiplied by the number of bytes. A share holding 200,000 folders of small documents takes far longer than one holding 200 folders of video, even if the video share is ten times larger.
Three things shorten it. Scan from a wired machine near the server, since Wi-Fi adds latency to every one of those requests. Scan one share rather than the root of the NAS. And if the NAS has its own storage analyzer in its web interface, run that for the overview, because it walks the disk locally at full speed, then scan only the share you intend to clean from Windows to get paths your colleagues can act on.
Every support ticket about a slow scan turns out to be a share over Wi-Fi with a few hundred thousand folders. The tool is fine. Plug in a cable and scan the one share that is full. It finishes in the time it takes to make a coffee.
Which Disk Space Tools Handle Network Drives?
All the well-known ones accept a mapped letter or a UNC path, so the question is what changes when they do. WizTree keeps working but loses its main advantage: its own site explains that the MFT read applies to NTFS drives and that non-NTFS and network drives are scanned by another, slower method. It also needs a paid licence for business use, share or not. WinDirStat scans a UNC path with its usual folder walk and writes a CSV afterwards, and being open source it is fine on a company machine. The WizTree and WinDirStat comparison has the detail on both.
TreeSize Free is the one to read carefully. JAM Software's page for it says it shows sizes on local drives as well as network shares and names Synology, QNAP and Western Digital NAS units as supported, then says that scanning network drives in commercial environments is not possible with TreeSize Free and points at TreeSize Professional. The software does not stop you. The licence does. Univik Disk Usage Reporter scans a share through Scan a Folder in its free edition with no private-use clause, and adds the HTML report, which on a shared drive is usually the point of the exercise.
External and Network Drive Support Compared
The rows that matter on a share are the last three: whether you get a report with paths, whether you may use the tool at work and the fact that no tool sees past your own permissions.
| Question | Univik Disk Usage Reporter | WizTree | WinDirStat | TreeSize Free |
|---|---|---|---|---|
| External USB drive | Yes, from the home screen | Yes, MFT speed if NTFS | Yes | Yes |
| Network share or NAS | Yes, via Scan a Folder | Yes, slower folder walk | Yes, UNC path | Yes, private use only |
| Scan speed on a share | Set by the network | Set by the network | Set by the network | Set by the network |
| Report with full paths | HTML and CSV | CSV | CSV | PDF in Free |
| Allowed on a company share | Yes, free edition | Paid licence for business use | Yes | TreeSize Professional needed |
| Sees folders your account cannot open | No | No | No | No |
Univik Disk Usage Reporter takes any drive letter or a folder path including a mapped share, ranks the folders, lists the biggest files with full paths and writes the HTML or CSV report. Free edition, allowed on work machines, nothing leaves your network.
Windows 7 to 11 · USB and mapped drives · scan speed on a share depends on your network
The short version
- An external USB drive scans like an internal one. Pick its letter and go.
- A network share scans through a mapped letter or UNC path, one share at a time, from a wired PC near the server.
- Network scans are slow because each folder is a round trip. Folder count and latency set the time, not gigabytes.
- WizTree loses its MFT speed on shares and needs a business licence. TreeSize Free may not be used on company shares. WinDirStat and Univik are fine at work.
- Export the HTML and CSV before you disconnect, and use the NAS's own analyzer for the whole-box overview.
Scan a share with the free disk usage reporter
Network Drive Questions
About This GuidePrepared by Leena Taylor Paul for Univik, a Windows utilities maker since 2013. The WizTree scan-method statement and the TreeSize Free network licence wording were taken from the vendors' own pages in September 2026. Timings come from scanning a USB 3 external drive and a mapped SMB share on a gigabit office network with Univik Disk Usage Reporter. 22 September 2026. Share scan stalling? Support will ask how many folders it holds and if you are on Wi-Fi first.
Sources: WizTree: how scanning works · JAM Software: TreeSize Free and network drives · Univik Disk Usage Reporter