fast-copy vs Robocopy
Robocopy ships with Windows, which makes it the default answer for scripted copies — and for some jobs it should stay that way (see the honest section below). But it reads files in directory order, never verifies what it wrote, and its multi-threaded mode can actually hurt on rotational disks by turning sequential reads into seek storms. fast-copy sorts reads by physical offset (FSCTL extent mapping on NTFS), bundles small files, and hash-verifies every file — while still finishing first.
The measured difference
Windows 11, USB HDD to internal SSD (NTFS), full reboot before each run, standby list purged with RAMMap, Windows Defender active for all tools:
| Tool | Time | Verifies output? |
|---|---|---|
| fast-copy | 2 m 28 s | yes — every file, by hash |
| robocopy /MT:1 | 3 m 16 s | no |
| robocopy /MT:8 | 3 m 44 s | no |
Note the /MT:8 result: more threads made robocopy slower on this rotational source — parallel reads defeat the disk's sequential access pattern. Full methodology and exact flags here.
Feature differences that matter
| fast-copy | robocopy | |
|---|---|---|
| Ships with Windows | no — single exe download | yes |
| Read order on disk | physical-offset sorted (FSCTL) | directory order |
| Post-copy verification | on by default (per-file hash) | none |
| Content dedup → hard links | yes (NTFS hardlinks, ReFS block clones) | no |
| Pre-flight space check | yes | no |
| Copies to Linux/NAS over SSH | yes — tar pipe, no SFTP | no (SMB paths only) |
| Long paths (>260 chars) | yes (\\?\ prefix) | yes |
When Robocopy is still the better tool
Honest answer: when you cannot install anything — locked-down servers, scheduled tasks on machines you don't control — robocopy's zero-install advantage is real. Its /MIR mirroring with attribute filters and its retry/wait semantics (/R /W) for flaky network shares are also mature and battle-tested. If those are your constraints, keep robocopy; if raw speed and verified output matter more, that is what fast-copy is for.
Download fast-copy · Windows install & SmartScreen notes: /install/windows/
Also compared: fast-copy vs rsync · fast-copy vs cp · fast-copy vs scp / SFTP · fast-copy vs FastCopy · fast-copy vs TeraCopy · full benchmark methodology