[Samba] ceph_vms performance

[David Disseldorp]

Hi Tom,

On Wed, 23 May 2018 09:15:15 +0200, Thomas Bennett via samba wrote:

> Hi,
> 
> I'm testing out ceph_vms vs a cephfs mount with a cifs export.

I take it you mean the Ceph VFS module (vfs_ceph)?

> I currently have 3 active ceph mds servers to maximise throughput  and
> when I have configured a cephfs mount with a cifs export,  I'm getting
> a reasonable benchmark results.

Keep in mind that increasing the number of active MDS servers doesn't
necessarily mean that you'll see better performance, especially if the
client workload is spread across the full filesystem tree, rather than
isolated into the corresponding sharded MDS subdirectories.

> However, when I tried some benchmarking with the ceph_vms module, I
> only got a 3rd of the comparable write throughput.
> 
> I'm just wondering if this is expected, or if there is an obvious
> configuration setup that I'm missing.

My initial assumption would be that the improved CephFS kernel mount
performance is mostly due to the Linux page cache, which is utilised
for buffered client I/O.

Cheers, David