some thoughts about gmirror

Mike Wolman mike at
Sat Apr 7 09:35:58 UTC 2007

Rsync is a great tool however if you try to rsync a filesystem
with hundreds of thousand files in it the file list can use quite
a large amount of bandwidth even if only a single file has
changed - if you were keeping track of the blocks which had changed
then you do not need to generate this list and simply send over the
changed blocks.

I was not thinking the remote side would mount the image unless
the primary site was offline/unavailable.


On Fri, 6 Apr 2007, R. B. Riddick wrote:

> --- Mike Wolman <mike at> wrote:
>> It could also be used for asynchronous mirrors over slow links, if the log
>> device was always written to first then the write latency for long distant
>> links could be removed.  Im not sure if it would be possible to achieve
>> this using just a modified ggatec instead which has a local device used
>> as a write cache.
> Sounds like rsync can already do that (I am not sure right now, if rsync can
> find updated areas within a large file, or if it just copies the while updated
> file even if it is a large one)...
> Furthermore the remote consumer of that gmirror couldnt be mounted RW, if it
> uses UFS, because UFS doesnt allow multiple RW mounts at the same time...
> -Arne
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