Storage Heartbeat on vSphere 5.0, 4.1, and 4.0

Note: This recommendation for using Storage Heartbeat applies only vSphere 4.1 and 5.0. It is not necessary with vSphere 5.1.
In the VMware virtual networking model, certain types of vmkernel network traffic is sent out on a default vmkernel port for each subnet. If the physical NIC that is being used as the uplink for the default vmkernel port goes down, network traffic that is using the default vmkernel port will fail, including vMotion traffic, SSH access, and ICMP ping replies.
Even though iSCSI traffic is not directly affected by this condition, a side effect of the suppressed ping replies is that the EqualLogic PS Series Group will not be able to accurately determine connectivity during the login process, and therefore a suboptimal placement of iSCSI sessions can occur. This could cause logins to not be completed in a timely manner.

It is recommended to have a high availability vmkernel port on the iSCSI subnet serving as the default vmkernel port for such outgoing traffic.

Also see this related blog article.

You would want the lowest numbered VMkernel port on that network to not have an iSCSI bind.
Assuming you have four VMkernel ports on one vSwitch with four physical nics and a one-to-one iSCSI binding:
locate the lowest numbered VMkernel port (vmkx where “x” is the lowest number on that network)
make a note of the VMK name
make a note of the IP address
make a note of the physical nic it was bound to
unbind the vmk
change the IP address of this port to a new address on that network.
You may as well enable management on this VMK and rename it appropriately
Create a new vmkernel port and give it the IP address and name you noted earlier
Bind the new vmk to the pnic noted earlier

TR1074-Configuring-MEM-1.1-with-vSphere-5&4.1
TR1049 Configure vSphere SW iSCSI

As for ESX 5.x, TR1075 shows how to do this using GUI as well.
TR1075-Configure-iSCSI-Connectivity-with-VMware-vSphere-5

The key idea is to configure an additional VMKernel port that has the lowest vmk number with all 4 NICs assign to it (if it’s PS6000/6100 series)

However, how to easily reconfigure the original setting, things like rename the vmk number still reminds as a mystery, because it is quite troublesome for those who has already got everything setup and doesn’t want to have any maintenance window.

More info about this is available here: http://communities.vmware.com/message/2082335

It is also covered in the Dell Equallogic Tech Reports for configuring iSCSI with VMware ESX.

Also, yes disabling Delayed ACK for iSCSI is beneficial. It helps prevent additional latency. I suspect that not only Equallogic iSCSI arrays would benefit from disabling delayed ACK. There’s a KB article on it, on the Equallogic support website.

FYI: This is an issue in the ESX network stack. In the Dell/EQL tech reports it explains how a configuration change will prevent this probelm from occuring. Also, ESXi v5.1 is expected to have a permanent fix for this issue.

Btw, EQL said there will be a patch regarding this coming in Q1 2011, anyhow, it doesn’t really affect the redundancy at all, not sure about HP Lefthand though. Does it also affect connectivity? I understand vmkping won’t work, but iSCSI connection is still working right?