I am transferring a rather large video file across WAN using rsync. As you could expect, it doesnt have blazing speed. In the process of sniffing around trying to gain some bandwidth, I noticed some very strange behavior.
When resuming an rsync transfer with rsync -aP <source> <destination> , I saw rsync report very high transfer speeds (about 45 MBps) while it was doing the delta identification phase, comparing checksums of files. Then when it reached the part of the file I had stopped at previously, It would suddenly drop to 1/20th the speed. The most interesting part of all though was that the surge of traffic at the beginning was actually incoming data as seen in the pictures below.
Im baffled by this since iperf shows an average TCP bandwidth of 28 Mbps (about 3.5 MBps) over several tests. Where is this extra bandwidth coming from and running off to?? Thanks in advance :)