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Questions about rsync

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  Questions about rsync Spyridon Metaxas <SMet@somewhere.world> - 2019-06-24 15:02 +0000
    Re: Questions about rsync Dan Purgert <dan@djph.net> - 2019-06-24 15:08 +0000
    Re: Questions about rsync Grant Taylor <gtaylor@tnetconsulting.net> - 2019-06-24 09:09 -0600

#4430 — Questions about rsync

	An rsync client can specify a number of options to shape the file 
synchronization that it launches. One of those options is compression. 
Two questions on this:

	1. When rsync is launched over SSH, is this option passed down to 
the SSH transport, or is it totally independent? If the latter, we could 
have compression at the rsync protocol, and then compression at the SSH 
transport, right? This is probably not a good idea, but I am just 
interested to learn how things are done in this respect.

	2. Is the server allowed NOT to honor the compression request 
from the client? Again, taking SSH as a reference - it's just that I am 
more familiar with it than with rsync - the server is allowed to ignore a 
compression request from the client. Is an rsync server allowed to do so 
as well, or is it the case that the synchronization can't succeed if the 
server, for whatever reason, does not support compression?

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#4431

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Hash: SHA256

Spyridon Metaxas wrote:
> 	An rsync client can specify a number of options to shape the file 
> synchronization that it launches. One of those options is compression. 
> Two questions on this:
>
> 	1. When rsync is launched over SSH, is this option passed down to 
> the SSH transport, or is it totally independent? If the latter, we could 
> have compression at the rsync protocol, and then compression at the SSH 
> transport, right? This is probably not a good idea, but I am just 
> interested to learn how things are done in this respect.

It's possible to try (IIRC) -- but yes, doubly-compressing just burns
cpu cycles for the most part.

>
> 	2. Is the server allowed NOT to honor the compression request 
> from the client? Again, taking SSH as a reference - it's just that I am 
> more familiar with it than with rsync - the server is allowed to ignore a 
> compression request from the client. Is an rsync server allowed to do so 
> as well, or is it the case that the synchronization can't succeed if the 
> server, for whatever reason, does not support compression?

as far as I am aware, no.  Remember that the compression is merely
on-the-fly, somewhat equivalent to 

  tar -czvf -- list-of-files | nc server.com portno 

  (server) nc receive | tar -xf --


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-- 
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|_|_|O| Github: https://github.com/dpurgert
|O|O|O| PGP: 05CA 9A50 3F2E 1335 4DC5  4AEE 8E11 DDF3 1279 A281

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#4432

On 6/24/19 9:02 AM, Spyridon Metaxas wrote:
> 1. When rsync is launched over SSH, is this option passed down to 
> the SSH transport, or is it totally independent? If the latter, we 
> could have compression at the rsync protocol, and then compression 
> at the SSH transport, right? This is probably not a good idea, but 
> I am just interested to learn how things are done in this respect.

I don't think that the compression option is passed from rsync down to 
the underlying SSH transport.

Remember that SSH is one of multiple transports that rsync can use.

There's also a reasonably good chance that even if compression is 
enabled on the underlying SSH transport, anything that's compressed at a 
higher layer will receive little, if any, compression from the 
underlying SSH transport.



-- 
Grant. . . .
unix || die

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