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

[Kevin Korb]

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,
>>>
>>
>> -- 
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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)
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>> 	PGP public key available on web site.
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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.
~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,