poor rsync performance with specific Linux kernel version?

[Michael Doerner - TechnologyWise]

Hi all

I am new to this list but a happy rsync user for quite some time. Thanks
for this great tool.

We are experiencing very slow rsync performance when using it as a
backup tool for our server virtualisation "Proxmox VE"
(http://pve.proxmox.com/wiki/Main_Page).

I have searched for our issue and posted at the Proxmox forums (
http://forum.proxmox.com/threads/6175-rsync-%28host%29-performance-issues-with-kernel-2.6.32-on-Supermicro-platform)
but no results so I hope to ask the question here properly:

Trying to rsync an 8 GB testfile (dd if=/dev/zero
of=/var/lib/vz/testfile_MDO bs=1024k count=8192 conv=fdatasync) on quite
a high-end system (Supermicro "X8DTI-F" board, 12 GB RAM, SAS disks on
Adaptec RAID controller) running Proxmox with a (Debian) Linux kernel at
that moment:

rsync --progress /var/lib/vz/testfile_MDO /var/lib/vz/testfile_MDO2
testfile_MDO
592379904 6% 949.34kB/s 2:20:24 ^C

I had to cancel due to the low speed at that time.

The issue seems related to the specific combination of hardware and that
particular kernel (Proxmox' "Debian" kernel 2.6.32). If I replace that
kernel with their alternative "Redhat" 2.6.18 kernel version, the same
rsync process is fast and will sync/copy the 8GB file in less than 2
minutes.

We can replicate the slow speed problem on two other servers which use
almost identical hardware. Can I get any help or idea here on this list
what I could try to further isolate this issue?

Regards,
Michael