Hi all,

we have a Lustre 2.4.3 with

- oss/mds: CentOS 6.5, whamcloud patched kernel
2.6.32-358.23.2.el6_lustre.x86_64
      (rpms from
http://downloads.whamcloud.com/public/lustre/lustre-2.4.3/el6/server/RPMS/x86_64/)

- client: sles11sp1, kernel 2.6.32.36-0.5-default, patchless client
from http://build.whamcloud.com/job/lustre-b2_4/74/arch=x86_64,build_type=client,distro=sles11,ib_stack=inkernel/

We are experiencing problems with basic I/O commands like `dd` and `cp`.

When we write with `dd`, from a client running SLES11 SP1, *without
direct I/O*, we got about ~40MB/s throughput.
When we try with direct I/O (dd oflag=direct), we have the expected
performance (220-240MB/s thriughput).

If we run the exact same tests using a CentOS 6.5 with whamcloud
patched kernel 2.6.32-358.23.2.el6_lustre.x86_64, we got the correct
performance regardless of direct-I/O or non-direct I/O .

We guess there is a problem with the kernel version we are using on
our clients. Is there something known about this behaviour?

Thanks,
Francesco