On 1/19/2011 11:41 AM, Ed McDonagh wrote:
>
>>> Isn't someone going to mention checksum caching to save processing on
>>> the backup server side?
>>
>> Thanks for doing so. Perhaps you could explain?
>>

> http://backuppc.sourceforge.net/faq/BackupPC.html#rsync_checksum_caching
>
> Basically add --checksum-seed=32761 to both the RsyncArgs and the
> RsyncRestoreArgs.
>
> Without this option, each file on the backuppc side needs to be
> uncompressed and the checksums are calculated to send to the client for
> comparison. Therefore there is a lot of disk i/o and processor use
> without actually transferring any file data because nothing has changed.
>
> With this option, the checksums are cached on the server side, thus
> removing the disk i/o and processing. This still needs to take place on
> the client side, but without the decompression step.
>
> There is also a $Conf{RsyncCsumCacheVerifyProb} setting with a default
> value of 0.01, which means that 1% of the time the cache checksums are
> verified.

Note that this mostly affects full runs where the --ignore-times option 
is added so all files have the checksum comparison repeated.  Also, it 
won't have any affect until the 2nd or 3rd run after setting the option.

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com


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