When I try to continue the upload of a very large file (400GB, 200GB already transmitted) with --partial, rsync stops with an error after 10 minutes. Verbosity shows, that during this time it has transmitted checksums for about 30G worth of data. Increasing the timeout with --timeout=100000 helps. With this, rsync reaches the point where it transmits new data.
These bugs seem to be related (having similar error messages: connection unexpectedly closed, broken pipe, timeout). bug7757 with big file, rsync times out out when it should not; the sender is still responsive bug2783 Random high loads during syncs (server side) / client stream errors rsync: connection unexpectedly closed (2761332 bytes received so far) [generator] rsync error: error in rsync protocol data stream (code 12) at io.c(365) bug5478 rsync: writefd_unbuffered failed to write 4092 bytes [sender]: Broken pipe (32) rsync: writefd_unbuffered failed to write 4092 bytes [sender]: Broken pipe (32) io timeout after 30 seconds -- exiting rsync error: timeout in data send/receive (code 30) at io.c(239) [sender=3.0.2] bug5695 improve keep-alive code to handle long-running directory scans ./io.c:void maybe_send_keepalive(void) bug6175 write last transfer status when timeout or other error happens rsync: writefd_unbuffered failed to write 4 bytes [sender]: Broken pipe (32) rsync: connection unexpectedly closed (99113 bytes received so far) [sender] rsync error: unexplained error (code 255) at io.c(600) [sender=3.0.5] bug7195 timeout reached while sending checksums for very large files
I ran into a similar issue recently while transferring large files (>40GB). After a few tests, it seems - in my case at least - to be related to the delta-xfer algorithm. The bug does not happen anymore with the -W option. I don't know if this will resolve your issue, but you can also try looking into these options : --no-checksum --no-compress --blocking-io. These were not the source of my problems, but the functions they're related to might rise a network timeout. I hope it helps, anyways, good luck solving your issue.