Ceph support for Direct I/O

[Chang]

Hi,

I was trying to test write performance of Ceph, using direct I/O.

$ dd if=/dev/zero of=/mnt/ceph/my.dat bs=1M count=1 oflag=direct

But dd is just stuck without doing any write.

Without oflag, write is done fine.

In the above example, I used Ceph kernel module 0.20, built on kernel 2.6.32.

I also tried Ceph fuse client to mount.
In this case, the above dd command gives me:

"dd: opening `/mnt/ceph/my.dat': Invalid argument"

Is it because Ceph does not support direct I/O?

I'm using ceph 0.46, installed using Debian release package.
There are three OSDs, 1 Mon and 1 MDS in the cluster.

Any help or clarification is appreciated.

Chang