Pre-allocation means a download occupies its full size from minute one

A torrent client can use far more space than the files it has actually downloaded, for three reasons that all look like bugs and are all deliberate.

The three causes

• Pre-allocation. Most clients reserve the full size of a file when the transfer starts, so a 40 GB download occupies 40 GB from the first minute.
• Separate incomplete folders. Clients download to one folder and move to another on completion, and an interrupted transfer stays in the first one forever.
• Copy instead of move. If the two folders are on different drives, completion copies rather than moves, and the original may remain.

Finding what is actually there

Get-ChildItem "$env:USERPROFILE\Downloads" -Recurse -File -EA SilentlyContinue |
  Where-Object { $_.Name -match '\.!qB$|\.part$|\.!ut$' -and $_.Length -gt 100MB } |
  Sort-Object Length -Descending |
  Select-Object @{n='GB';e={[math]::Round($_.Length/1GB,2)}}, FullName

Those extensions are the incomplete markers used by the common clients. Anything on that list from more than a few weeks ago is a transfer that will not resume, holding its full pre-allocated size.

Seeding, and the second copy

Files you continue to seed are files you are keeping, which is the point, and people forget them because the client is minimised to the notification area. Check the client's own list rather than the folder, and remove torrents through it so the data goes with them.

The settings worth changing once

1. Turn off pre-allocation if you download over unreliable connections and abandon transfers.
2. Put incomplete and complete folders on the same drive, so completion is a move rather than a copy.
3. Set a seeding ratio limit so torrents stop being kept indefinitely.
4. Point the download folder at a second drive if this is regular.

The Downloads folder itself collects everything else at the same time, which is worth the same pass and is the easiest space on any machine.