Possibility to run rsync without hash table lookups

[Michael Lynch]

I really like rsync's ability to replicate block level changes to the second
system, using --inplace.
I think the function is more powerful than the documentation might elude to.


For example, lets say I had a block-level backup program performing
incremental daily backups on my backup server.
RSync's --inplace option suits this really well.

But it would be nice if large file performance could be improved.
In respect to the data I have, there is no need to go through the data twice
or thrice. And I only have an Atom... :)

There is a Linux project called Zumastore that performs block level
replication (in real time)
But rsync has the ability to do this on a drop-in file level basis, and also
on cross-platform.

Would it be a feature worth considering?
Am I correct in assuming that RSync is using a hash table to find matching
blocks?
(Something is chewing up the little Atom's core!)

RSync already has what I might consider miscellaneous features.
One of which, the --append-verify option, I find quite dangerous, and not
much safer than --append:
 - append-verify first transfers the 'appended' portion of the data, and
then does a verify
 - If the verify step fails, then it does a full normal rsync on the file
 - IF, at this point, rsync is interrupted (for any one of it's sensitive
reasons), then the next time the job runs, the file will be ignored!
(because the mod date and size are the same)
To use append-verify safely, you would have to use --checksum, or indeed you
must just be sure you really do have append only data.

Michael.


On Tue, Jul 26, 2011 at 1:24 PM, Wayne Davison <wayned at samba.org> wrote:

> On Mon, Jul 25, 2011 at 1:42 AM, Michael Lynch <michaellynch511 at gmail.com>wrote:
>
>> Is it possible to disable hash table look ups, but still have the MD5
>> block comparison?
>>
>
> You can use --checksum (-c) to check file contents to see if they need to
> be transfered, and you can turn off the incremental-content updating via
> --whole-file.  There is nothing else beyond that.
>
> ..wayne..
>
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