sshfs is slow over a WAN: 1.33 MB/s at every file size

Why is sshfs so slow over a long link? We mounted a Singapore server on a Timisoara server with sshfs, about 200 ms apart, and read files with dd. A 100 MB file came in at 1.32 to 1.34 MB/s over ten trials. A 1 GB file came in at 1.33 MB/s over five. When the rate stays the same at every file size, the round trip sets the speed: each trip carries a fixed amount of data, and a bigger file only adds more trips. KeibiDrop read the same pairing on demand at 20 to 30 MB/s, because it keeps several blocks in flight at once. This post has the setup, the arithmetic, and the one variable we did not capture.

Measured, with the conditions on the original page:

• sshfs, 100 MB file | n=10 | 1.32 to 1.34 MB/s, median 1.33
• sshfs, 1 GB file | n=5 | 1.33 MB/s, flat
• KeibiDrop on demand, same pairing | n=5 | 20 to 30 MB/s

Full version, with the limits and the method: sshfs is slow over a WAN: 1.33 MB/s at every file size

Source, MPL-2.0: github.com/KeibiSoft/KeibiDrop