increasing the write block size for high latency

A publicface at
Mon Jul 7 18:00:47 MDT 2014

I'm going to be interested in the answer to this question one of these 
days real soon, so I did some googling and found this blog:

He talks about eliminating ssh and just using rsyncs own protocol to 
speed up the transfer.  I read elsewhere that the encryption is what's 
slowing it down - which makes sense to me.

Disclaimer: I don't know anything about the author, the blog, rsync or 
sshd other than what I read for the most part.   So if someone else 
comments with other solutions, they almost definitely know more about it 
than I do.

P.S.  The author makes an appeal to developers I hope rsync will become 
more smart in the future and allows the combination of “|--inplace 
--sparse|” or can even autodetect the best strategy." in regard to KVM 
files - which sounds good to me.  YMMV

On 07/07/2014 01:18 PM, Adam Edgar wrote:
> I am trying to transfer a group of files in whole using rsync using the —files-from option across a network with high bandwidth but relatively high latency. When I log into the remote machine I see an rsync command running like thus:
> rsync --server --sender -Re.sf -B16384 --files-from=- --from0 . /
> Note that I have used the -B option to increase block size but that seems to just apply to the blocks used for checksumming instead of actual network I/O. I came to this conclusion by running strace on the PIDs on both remote and local hosts. On the server side I got a stream of 4K writes on fd 1 followed by a select on that same fd :
> write(1, "\275\214\357\357\22y4\237\215Z\226\331\355Z!\340\373\227\340V~\20\35C\3\337_\27\257\236\321\204"..., 4092) = 4092
> select(2, NULL, [1], [1], {60, 0})      = 1 (out [1], left {59, 999996})
> I’d like to see if I can increase the write block size to cut down on the delay of each select to this unnamed pipe to sshd.  I’m not sure if that would help speed up the transfer as the issue may be below at the sshd level (which I can’t strace as a non-root user).  If anyone has experience with slowness at the ssh level please advice on which flags would allow me to speed up there.
> Any help will be much appreciated.
> Adam S Edgar

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