CIFS single connection speed limit issue

Hi

We are experiencing CIFS write throughput issues on a CX4-480 that had a Celerra head installed.

2 DM’s, Active Passive with 1 VDM. 2x 10GbE interfaces on each DM in a LACP channel  ToR Switch

We have one FC Raid5 set presented and 1 SATA Riad6 set presented

From a server attached to the same ToR switch, same VLAN, with 2 x 10GbE connections we can only achieve 25MB/s on a single CIFS write connection. The speed doesn’t change when writing to FC or SATA. If a 2nd and 3rd write stream is established, throughput effectively doubles, triples respectively

MTU was at 9000 and set back to 1500 with a slight increase – weird

Files being written range from 20GB to 100GB

DMs and server have been set to a single 10GbE connection, same speed on a single connection

VDM was deleted and CIFS server set up on Physical DM, same speeds

Analyser  shows the disks are not under load, SPs are at 50-60%

Celerra CPU and Memory are fine, not stretched

Is there a setting to increase the throughput on a single CIFS connection?

Cheers

Mike