[CentOS] evaluating backup systems: rsync
Nicolas.Thierry-Mieg at imag.fr
Sat Jan 19 19:29:02 UTC 2013
Reindl Harald wrote:
> Am 19.01.2013 19:28, schrieb Nicolas Thierry-Mieg:
>>>> no I don't think you will, since the file modification times won't have
>>> and even if the did - who cares?
>>> * rsync does not transfer unchanged data ever
>>> * rsync will sync the times to them from the sources
>>> * so have nearly zero network traffic
>> Not true: if you change the modification time on a file, by default
>> rsync will copy the whole file again.
>> See man rsync:
>> Rsync finds files that need to be transferred using a “quick check”
>> algorithm (by default) that looks for files that have changed in size or
>> in last-modified time.
>> and yes I've tested this before posting ;-)
>> to avoid this you need to use --size-only
> yes it transfers - but with rsync algorithm
> RTFM how rsync works - it will generate checksums on both
> sides, tnrafser only the checksums and come to the conclusion
> that the data are ident
> i am using rsync since many years for all sort of backups
> and file transfers and even my thunderbird-profiles over
> WAN is copied with a "virtual speed" of 200 Megabytes per second
> [harry at srv-rhsoft:~]$ ls /mnt/data/profiles/thunderbird/harry/global-messages-db.sqlite
> -rw-r----- 1 harry verwaltung 640M 2013-01-19 19:31 /mnt/data/profiles/thunderbird/harry/global-messages-db.sqlite
> this file will ALWAYS be changed, not only modification times
> but that does not change the facht 99.8% of the file is unchanged
> and rsync by design transfers only the changes over the wire
> since i am doing this DAILY between home and office machine
> you do not need to explain me how rsync works and in which cases
> in trafsers data - really you do not need
> i sync some TB of data daily inclduing GB large logfiles
> where is also only the new part transferred all the time
chill out dude...
again, read the man page. This is not true if source and dest are local:
then the rsync algo is not used, and if the mod time is changed on the
source the whole file will be copied.
so if you're rsyncing locally, eg to a usb drive, you need --size-only
as I said.
Now if one of the source or dest is remote I agree with you, but this is
not alwayss the case. I don't recall whether the OP expressed whether
that was the case or not, though I think he mentioned wanting to backup
family pictures, so it might very well be to a usb HD. Inany case I
definitely know you mentioned testing things locally. Which I did, and
being wrong is ok, but you should really work on that attitude of yours.
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