paul+rsync at wurtel.net
Mon Sep 24 17:16:27 GMT 2007
On Mon 24 Sep 2007, Stephen Zemlicka wrote:
> I am having trouble running rsync over a mapped drive. Basically it only
> copies whole files. I use the -rvcS switches. Any suggestions?
>From the manpage:
With this option the incremental rsync algorithm is not used and
the whole file is sent as-is instead. The transfer may be
faster if this option is used when the bandwidth between the
source and destination machines is higher than the bandwidth to
disk (especially when the "disk" is actually a networked
filesystem). This is the default when both the source and des-
tination are specified as local paths.
This is because there's no advantage to updating only parts instead of
the whole file. If rsync finds it needs to update a file, it now only
has to read the source, write the destination (via a temp file so that
the destination filename either points to the old version or the new
version; not an incomplete new version. If you want that, use
If it did it incrementally, then rsync would need to read the source,
read the old destination file, compare, and while writing the new temp
file read from either the source or the old destination. This is more
IO, and hence less efficient.
Rsync's incremental algorithm is for optimizing network traffic at the
expense of more local disk IO, in the assumption that the network is
slower than local disk IO. If you're doing a local transfer, it
optimizes the disk IO... Using a mapped drive appears to be a local
disk. If you can transfer directly between the server from which the
drive is mapped instead of going through the mapping, then that's
preferable (and will decrease network traffic...).
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