[Bug 8512] rsync -a slower than cp -a

[samba-bugs at samba.org]

https://bugzilla.samba.org/show_bug.cgi?id=8512

--- Comment #3 from Sandon <sandon at van-ness.com> 2011-10-07 17:45:53 UTC ---
I am seeing performance problems as well but CPU bottleneck. My issue is even
cp is CPU bottlenecked and dd with direct i/O gives me the best performance.

Nobody mentioned -W before but it didn't seem to make a difference for me.
Copying a file from one array to another I am seeing the following:

cp (no direct I/O) 94% cpu = 1min11s
rsync (no direct I/O) 210% cpu = 2m41s
rsync -w (no direct/IO) 205% cpu = 2m46s
dd (direct I/O) 13% cpu = 47s
dd (no direct I/O) 85% cpu = 1m24s
cp (libdirectio) 114% cpu = 50s

so my best bet is cp with libdirect I/O but I am not fond of this method as it
also is using a lot of CPU usage. I wish there was something that could give me
the speed/CPU usage of dd with direct I/O. Pushing data through the memory
buffer on my machine is eating up too much CPU usage and bottlenecking the
transfer in my case.

I don't know if rsync does check-suming  and stuff and that is why it seems to
be the slowest out of everything I tested.

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