We have an MD3000i array accessed by three separate servers (all blade servers accessing through chassis nic's). Controller 1 (both Ports 0 and 1) are linked to Server A. Servers B and C (both with substantially less activity than Server A) are linked to Controller 0 (Ports 0 and 1). Server A is on a separate VLAN (connected to the MD3000i through a switch on the back of the blade chassis), and Servers B and C are on their own VLAN (also connected to the MD3000i through a switch on the back of the blade chassis).
The problem we are running into is that Server A has decidedly better read throughput from the MD3000i. For instance, when looking at backup jobs run through that server, the job rate is roughly 3,000MB/min. However, when looking at backup jobs run through Servers B or C, jobs rates are as low as 200MB/min.
If I view the iSCSI MAC transmit statistics through the MDSM, there are very different readings between controllers (aside from overall volume):
Mac transmit statistics MAC transmit legend F = Frame Count B = Byte Count MF = Multicast Frame Count BF = Broadcast Frame Count PF = Pause Frame Count CF = Control Frame Count FDF = Frame Deferral Count FED = Frame Excess Deferral Count FLC = Frame Late Collisions Count FA = Frame Abort Count FSC = Frame Single Collision Count FMC = Frame Multiple Collisions Count FC = Frame Collision Count FDR = Frame Dropped Count JF = Jumbo Frame Count iSCSI Host | Port | F | B | MF | BF | PF | CF | FDF | FED | FLC | FA | FSC | FMC | FC | FDR | JF Controller 0 | port 0 | 440573739 | 651904980400 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 Controller 0 | port 1 | 440549412 | 651892177000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 Controller 1 | port 0 | 109676946034 | 148467634266838 | 0 | 0 | 512 | 131072 | 512 | 1024 | 1024 | 1024 | 512 | 1792 | 2304 | 2304 | 589824 Controller 1 | port 1 | 402653242 | 111669157090 | 524288 | 524288 | 2304 | 720896 | 2304 | 3328 | 3840 | 4352 | 2048 | 3584 | 5632 | 2048 | 1114112
My suspicion is that the network card utilized by Servers B and C doesn't have the capabilities needed to achieve the performance we are looking for (notice that the Jumbo Frame count is 0 -- Jumbo Frames being something I've seen recommended when multiple servers are accessing a single MD3000i controller). Server A accesses the MD3000i through a Broadcom BCM57085 NetXtreme II, while Servers B and C access the MD3000i through an Intel PRO/1000 MB Dual Port.
As of now, I don't have a firm method for isolating the cause of the slow read throughput on Controller 0 (Servers B and C).