Speed problem

Craig Barratt craig at atheros.com
Tue Nov 12 05:39:00 EST 2002

> > > You haven't really provided enough data to even guess what
> > > is limiting your performance.

How similar is the directory tree on the target (receiving)
machine?  There are three general possibilities:

  - It's empty.

  - It's present, and substantially similar to the sending end.

  - It's present, but substantially different to the sending end.

In the first case rsync should be i/o limited (disk or network).

In the second and third cases rsync could easily be cpu limited
on the sending end.  In the third case it could also be disk
(specifically seek) limited on the receiving end.  For example,
you might dump a large database to a binary file, whose content
(records) are similar, but the order might change dramatically.
This could take a huge number of seeks on the receiving machine
to rebuild the file, even though only a small amount of data is

Unless I'm missing something, the behavior you observe could simply be
rsync hitting files (or directories) that are in the different
categories above.

I'd try adding the -v option and see if the "slowdown" always
happens on certain files.  Then try running rsync on just those
files.  If it is slow right away then maybe this explanation is
correct.  If it still goes fast, then slows down, then there
is something else going on.

As another test, run rsync to an empty target directory.  Rsync
should be i/o limited for the entire running time.


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