Tony Schreiner wrote:
> On Jul 3, 2008, at 4:07 PM, Evren Yurtesen wrote:
>
>> Renke Brausse wrote:
>>> Hello Tony,
>>>> I've written before about backups involving very big files that
>>>> seem to execute slowly.
>>>>
>>>> What can be slowing things down so much? Except for this
>>>> operation, everything else runs about as I would expect.
>>> I have no clue what the reason is but I experienced that backups of
>>> large files are much faster with tar over ssh instead of rsync
>>> over ssh.
>>> Not an explanation but maybe this can solve your problem.
>> I believe the reason for this is how rsync works. It normally tries
>> to transfer only the changed parts of the file. This is to save
>> bandwidth, to do this, it has to scan the whole file on both sides
>> (I guess). This is unnecessary unless you are over slow links. You
>> might want to try the whole-file option with rsync:
>>
>> -W, --whole-file copy files whole (w/o delta-
>> xfer algorithm)
>>
>> Please let us know the results, as a side-note if you still want to
>> shrink the transferred file size you can use the ssh compression
>> with -C option of ssh.
>>
>> Thanks,
>> Evren
>
>
> Reporting back on this. Using the -W option did not make much
> difference. The dumps in question continue to run for a long time and
> eventually fail with an ALARM.
>
> For the time being I am excluding the really large files in question.
> I may try tar instead of rsync at some point as was suggested.
>
> Tony Schreiner
Are you sure that -W option was active for sure? Did you check with ps
axwww to be sure? or just took it granted that it was active?
Just asking because I have made several times similar mistake myself :)
By the way, if you are using compression, also enabling
--checksum-seed=32761 will make a dramatic speed difference. (although
manual suggests that this can be visible only on 3rd full backup).
Thanks,
Evren
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