Chunksize for SFTP over Internet?

#1

Hello.
I’m using the default chunk-size and seeing bad performance.
I also use encryption if that matters.
Source computer is using around 2% CPU for the duplicacy process.

Duplicacy:

I get around 5MB/sec on a 100Mbit connection. I tried increasing number of threads but that strangely enough does not seem to have any effect.

SFTP-transfer benchmark

If I transfer a 2GB file with WINSCP between the same endpoints, I get around 11MB/sec.

Question:

What is a viable chunksize? I guess the 4M default size was chosen for a reason? Will a larger chunksize help my transferspeeds?
Or can I tweak something else? Can I change the chunksize after init?

#2

Update:

I started another repo + backup to the same destination.
The first backup has now increased to around 8.9 MB/sec and the second one is going at 11.65 MB/sec

This seems really strange since my max physical speed is 100MBit ~=12.5MB/sec.

Does the “speed” output in duplicacy take dedup into consideration?

#3

SCP is generally faster than SFTP because the SCP protocol is more efficient.

Yes, the uploaded speed reported by Duplicacy actually takes compression and deduplication into account and therefore is higher than the actual upload speed.

Increasing the chunk size may increase the upload speed, because that usually means less overhead per chunk, but then the deduplication ratio would drop. With a 100Mbit connection I would even suggest reducing the chunk size to 1MB for better deduplication (and then use multiple threads to see if it helps).

The chunk size can’t be changed after init.