FastCopyWhich buffer size is fastest? Values by drive type
1Open the settings dialog
In the main window choose Option → Options. The relevant fields are Main buffer size (MB) and the I/O-related checkboxes. Changes apply immediately to the next copy — no restart needed.
2HDD: use 1 MB and enable OverLap I/O
Since v5.11.0 the default buffer is 2 MB, tuned for SSDs. On mechanical drives, large buffers mainly enlarge the seek window; setting 1 MB and enabling OverLap I/O (read and write concurrently) typically measures 10–20% faster on mixed file sets.
3SATA SSD: keep the default, check parallel R/W
A 2 MB buffer with default settings is fine. The bigger win is leaving the parallel read/write behavior enabled for same-drive copies, which v5.9.0 turned on by default.
4NVMe: pre-allocate and run elevated
Enable the pre-allocate option so the destination file size is reserved before writing — this avoids allocation overhead mid-copy. Launching FastCopy as administrator removes extra permission checks. Together these can add another 10–30% on NVMe-to-NVMe copies.
Frequently asked
QWhy did my copies get slower after updating to v5.11?
The default main buffer changed from 1 MB to 2 MB. On an HDD that can measurably hurt; open Options and set the buffer back to 1 MB.
QDoes a bigger buffer ever help?
Occasionally, on very fast NVMe drives with huge single files. Test 4 MB or 8 MB against 2 MB with your own workload — gains are usually within a few percent.
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