do I always have to use either --checksum or --times ?

[Robin Lee Powell]

...

That's ...

Behaviour confirmed.  That is *not* cool.

On Fri, Jul 15, 2022 at 04:18:18AM -0400, Kevin Korb wrote:
> Yeah, unfortunately rsync's --checksum doesn't even employ obvious
> optimizations that the man page says it does.  There is no reason for it to
> checksum files that only exist on one end or are different in sizes yet it
> does.  Just try doing an rsync of a huge tree to an empty dir. You won't run
> out of space.  You will get tired of waiting for it to do something and
> abort it.
> 
> On 7/15/22 02:57, Robin Lee Powell wrote:
> > --checksum is only slower than re-copying if your network connection
> > between the hosts is similar in speed (or faster than) each host's
> > local disk access.
> > 
> > If local disk access is 10x your network link, it is definitely not
> > slower than re-copying.
> > 
> > Having said that, it really is *very* slow, and before you use it
> > you should have a clear situation in mind that makes it plausible that
> > two files could have the same size and last mod time and still not
> > have the same data.
> > 
> > Or, alternately, be in a situation where a bit flip would be
> > catastrophic.  Such situations are not common.
> > 
> > On Thu, Jul 14, 2022 at 04:26:48AM -0400, Kevin Korb via rsync wrote:
> > > You should almost never use --checksum.  It is slower than just re-copying
> > > everything.  You should almost always use --times (or --archive which
> > > includes --times).  Without this rsync is almost as dumb as cp.  Also, ssh
> > > has been the default --ssh for a long time.
> > > 
> > > On 7/14/22 04:22, Fourhundred Thecat via rsync wrote:
> > > > Hello,
> > > > 
> > > > I want to sync local folder to remote server. When I run follwing
> > > > command repeatedly, it always transfers everything each time again and
> > > > again:
> > > > 
> > > >     rsync --rsh='ssh' foo/ server:/foo/
> > > > 
> > > > does it mean I have to always use either --checksum or --times, to
> > > > prevent repeated transfer of files that have not changed ?
> > > > 
> > > > thank you,
> > > > 
> > > 
> > > -- 
> > > ~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,
> > > 	Kevin Korb			Phone:    (407) 252-6853
> > > 	Systems Administrator		Internet:
> > > 	FutureQuest, Inc.		Kevin at FutureQuest.net  (work)
> > > 	Orlando, Florida		kmk at sanitarium.net (personal)
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> > > 
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> -- 
> ~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,
> 	Kevin Korb			Phone:    (407) 252-6853
> 	Systems Administrator		Internet:
> 	FutureQuest, Inc.		Kevin at FutureQuest.net  (work)
> 	Orlando, Florida		kmk at sanitarium.net (personal)
> 	Web page:			https://sanitarium.net/
> 	PGP public key available on web site.
> ~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,