Why is my rsync transfer slow?

[dbonde+forum+rsync.lists.samba.org at gmail.com]

On 2016-01-24 20:39, Selva Nair wrote:

> Sorry for butting in, but hope this helps:
>
> The command line you posted earlier reads
>
>   % rsync -HzvhErlptgoDW --stats --progress --out-format="%t %f %b"
> /source/ /destination/
>
> I think Kevin is asking you write out that /source/ and /destination
> exactly as used on the command line so that one could understand what is
> going on better.

That doesn't make sense. Both the source and destination path contains 
simple alphanumeric characters, no more no less. Why would it matter 
whether the path is /abc/ or /def/ or even /123/?

  The issues you're facing are rather unusual so a more
> complete description may help figure what's going on. Sure, you can mask
> username/password etc but do not simplify source and destination paths.
>
> Also the the description "The destination is a sparse disk image bundle
> mounted locally (but its
> "source file" is on a network storage)" is too cryptic. What kind of
> network storage? How is it mounted -- NFS? SMB? What kind of sparse disk
> image? What's a bundle?

It is exactly as I wrote. On a network volume (A) a "sparse disk image 
bundle" (B), i.e., a type of disk image used in OS X, is stored. B is 
then mounted locally (i.e., local to where rsync is run) on a computer 
(C) where it appears as one of many volumes.

In other words, B is stored on A. A is then mounted (using AFP) on C. C 
then mounts B (=opens a file on a network volume, but instead of opening 
e.g., a spreadsheet in Excel, opening B shows a new volume on the 
desktop of C) stored on A. The computer where it is mounted just sees a 
mounted volume - it can't distinguish between a disk image stored 
remotely or stored on the computers internal hard drive.

I assume you are familiar with the idea of disk images?