Hoping there are some people with good experience implementing iSCSI on a EMC Clariion CX4's.
Basically the problem is excessive amount of outbound discards on the switchports connected to hosts in an iSCSI environment.
A brief overview of the configuration...
- 2 x 10Gb ports per SP (different subnet per port, with 2 subnets across entire SAN)
- 2 x Catalyst 3750X in a Stack (dedicated to iSCSI, no VLAN's configured, all ports native VLAN 1)
- Server 2008 R2 connected using 2 x Intel ET adapters
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Cisco Catalyst 3750X
Server (Microsoft iSCSI)
Port counters on the switch interfaces connected to the server are showing a high amount of outbound discards particularly when performing large sequential reads from the SAN (backups etc). My theory is that the SAN is sending data at 10Gb speeds (although obviously determined by the disks in the back-end) which is overwhelming the capabilities of the 1Gb ports. SNMP on the switch is not showing that the 1Gb ports are being overutilized but I suspect this could be microburts which are not displayed by SNMP monitoring.
My question is, if the problem above is an accurate diagnosis, how do you prevent the 1Gb ports from being overwhelmed by the 10Gb ports? I have 'flowcontrol receive desired' configured on the switch interfaces...will flowcontrol only function correctly if the ports are set to full auto-negotiation? The 1Gbps ports are set to full auto but the 10Gb ports on the SAN cannot be set to full auto and have to be configured to 10Gb. Also, not seeing any PAUSE frames in the show flow control command on the Catalyst.
Other factors to note are...
- Jumbo frames for 9000 bytes configured (can ping with packet size of 8972 when running ping -f to the SP ports from the Windows host)
- TcpDelAckTicks set to 0 in registry (emc150702)
- TcpAckFrequency set to 1 in registry (emc150702)
- iSCSIDisableNagle created in registry (emc150702)
I'm not expecting an answer from the limited detail I've provided above but really hoping I can get onto someone who has a lot of knowledge in this area so it points me in the right direction.
Thanks in advance for your help!