rsync - Dec 2016 - Aw: rsync show files changed during transfer - how?

i'm using rsync for backup and, as rsync can detect if files have vanished
during transfer, i wonder how rsync can tell which files got modified during
transfer (i.e. which are not consistent on the destination side after transfer)

apparently, rsync can't show that information? 

wouldn't that be an extremely useful feature if rsync could do another
additional mtime or even checksum comparison after each file transfer?

for example emc  networker notifies about "changed during save".
i'm curious wg rsync doesn't

regards
roland
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When rsync tells you that a file vanished it is reporting a real error
from the file system.  It saw a file that needed to be transferred but
when it attempted to read the file it got a file not found error from
the FS/OS.

There is no equivalent error for "hey, the file you were reading changed
while you were reading it".  Rsync would essentially have to read the
file twice and compare.

This is what LVM and similar forms of snapshots are for.

On 10/31/2016 07:36 PM, devzero at web.de wrote:
> i'm using rsync for backup and, as rsync can detect if files have
> vanished during transfer, i wonder how rsync can tell which files got
> modified during transfer (i.e. which are not consistent on the
> destination side after transfer)
> 
> apparently, rsync can't show that information?
> 
> wouldn't that be an extremely useful feature if rsync could do another
> additional mtime or even checksum comparison after each file transfer?
> 
> for example emc networker notifies about "changed during save".
i'm
> curious wg rsync doesn't
> 
> regards
> roland
> -- 
> Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail
> gesendet.
> 
> 
-- 
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At 17:00 19.12.2016, devzero at web.de wrote:
>>http://olstrans.sourceforge.net/release/OLS2000-rsync/OLS2000-rsync.html
>
><snipp> But the filename twice can happen under other circumstances;
if you've seen this happen, it's almost certainly because the file
changed during transfer. Rsync does no locking. Which means that: if you are
modifying a file while it's being transferred, then probably the checksum
will fail and it'll go round again. And if it goes around twice, and it
still fails, then it prints a message saying; Error, checksum failed, file
changed during transfer? And it's probably a file like a log file that's
being constantly updated and so the checksums didn't match because it's
never going to be able to get it exact; it means that what you've got on the
other end is something which will approximate some snapshot of the file, but
because it's not doing any locking, it can't guarantee that it's got
a particular snapshot of the file, because you can't have an atomic read of
the whole file. [31m, 49s] <snipp>
>nope, this is wrong, there is no message "checksum failed"
Actually rsync does that (from a log on our server):
...
PUBLIC_SERVER_BACKUP/wiki/data/index/i10.idx
WARNING: PUBLIC_SERVER_BACKUP/wiki/data/index/i10.idx failed verification --
update retained (will try again).
...
PUBLIC_SERVER_BACKUP/wiki/data/index/i10.idx

So it did recognize a change and synched it a second time. Don't know what
happens
if the file changes again though.
>to be a valuable backup solution, i`d like some networker a`like behaviour
which gives "file changed during save"
> 
>i wonder what`s so difficult for rsync to "look" at the timestamp
or checksum a second time after transfer and if it changed it should spit out a
warning....
> 
>isn`t this something which _could_ be implemented, if somebody is able to do
ist ?
Maybe it's a question of informational flags (-v, --progress, --stats etc).

bye  Fabi