Here's my test in a nutshell:
# ON WINDOWS: install Cygwin and enable cygsshd
ssh-host-config -y
# set up authorized keys, etc to make things easier
# LINUX: Create a 2GB random file on Linux:
dd if=/dev/urandom of=/tmp/bigfile.bin bs=1M count=2000
# WINDOWS: rsync "pull" to cygwin
LINUXHOST=mylinuxhost
rsync -Pva $LINUXHOST:/tmp/bigfile.bin /tmp/ # 100MB/s full
speed
rm /tmp/bigfile.bin
# LINUX: rsync "push" to cygwin (from Linux machine)
WINHOST=mywindowshost
rsync -Pva /tmp/bigfile.bin $WINHOST:/tmp/ # slow,
dropping to 4MB/s
I get the same results transferring the other direction (WIN -> LINUX): The
Cygwin remote endpoint is always slow.
On Tue Aug 24 2021, at 4:43 PM, Mark Geisert <m...@maxrnd.com> wrote:
> Chris Roehrig wrote:
>> I have a network of Windows, Linux and Mac machines and I use rsync to
>> synchronize various directories between them.
>> I'm trying to figure out why my rsync transfers are so slow (<4 MB/s) only
>> when the remote endpoint is Cygwin rsync over sshd (with both a Linux or
>> Cygwin rsync client). In all other scenarios, I get the full 100MB/s as
>> expected from gigabit ethernet. This has been an ongoing problem for me for
>> a couple of years over several Windows and Cygwin versions, and I'd like to
>> try to fix it.
>> If I run rsync --daemon --no-detach under mintty in the foreground on the
>> remote Windows endpoint, I get the full 100 MB/s transfers, so it seems
>> like it has something to do with rsync.exe running in the background under
>> the cygrunsrv+sshd service (which was installed normally using
>> ssh-host-config).
>> If I do:
>> pv /dev/zero | ssh $WINHOST "cat > /dev/null"
>> or even
>> pv /dev/urandom | ssh $WINHOST md5sum
>> I also get the full 100 MB/s transfers, so it doesn't look like sshd itself
>> is being throttled by bandwidth or CPU.
>> The machines have less than 15% CPU utilization while transferring, with
>> each of the 4 cores less than 30%, so it doesn't look to be CPU issue.
>> In Task Manager, sshd.exe and rsync.exe seem to be running normally using
>> only few percent CPU, and show Power Throttling=Disabled, Priority=Normal.
>> Setting their Priority to High doesn't seem to change things.
>> Looking in Resource Monitor on the remote endpoint, the network usage is
>> pretty much a flat horizontal line at about 18 Mbps (2.5 MB/s), so it sure
>> looks to me as if rsync is somehow being bandwidth-throttled when run in
>> the background under cygsshd.
>> It's almost as if rsync has an implicit --bwlimit override when it is run
>> from cygrunsrv+sshd (I've tried --bwlimit=0 on the client which makes no
>> difference).
>> Any ideas? Not sure where to go from here.
>
> You're not the first to report this. I don't have any quick answer. But can
> you give one or two simple examples of commands that give slow transfers in
> your environment? Simple like your 'pv' examples, if possible, using
> whatever method that works.
>
> ..mark
>
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