Your iSCSI subnetting is a possible cause here. Each port that you use on a controller needs a unique subnet from the other ports on that controller. The mirror port (on the 2nd controller) needs to match the subnet. I suggest you re-do your whole subnetting to match best practice and then see what it does for you. If you're short on subnets, I'd suggest something like this: SAN: Controller 0 iSCSI port 0: 192.168.230.101 (with a 255.255.255.128 subnetmask) Controller 0 iSCSI port 0: 192.168.231.101 (with a 255.255.255.128 subnetmask) Controller 0 iSCSI port 0: 192.168.230.201 (with a 255.255.255.128 subnetmask) Controller 0 iSCSI port 0: 192.168.231.201 (with a 255.255.255.128 subnetmask) Controller 0 iSCSI port 0: 192.168.230.102 (with a 255.255.255.128 subnetmask) Controller 0 iSCSI port 0: 192.168.231.102 (with a 255.255.255.128 subnetmask) Controller 0 iSCSI port 0: 192.168.230.202 (with a 255.255.255.128 subnetmask) Controller 0 iSCSI port 0: 192.168.231.202 (with a 255.255.255.128 subnetmask)   Server: vSwitch1: vmk1: iSCSI01: 192.168.230.130 (connecting to 0-0 and 1-0) (again with 25 bit subnetmask) vSwitch2: vmk2: iSCSI02: 192.168.231.130 (connecting to 0-1 and 1-1) (again with 25 bit subnetmask) vSwitch3: vmk3: iSCSI03: 192.168.230.230 (connecting to 0-2 and 1-2) (again with 25 bit subnetmask) vSwitch4: vmk4: iSCSI04: 192.168.231.230 (connecting to 0-3 and 1-3) (again with 25 bit subnetmask)   This is basically extending this Dell article on how to set up an MD3000i with ESX 4.0 for usage with an MD3200i.
Okay ... fresh off a weekend altering heart stopper so please bare with me if I ramble a bit :emotion-7: We recently had to add a MD3220i to our network as we were running out of disk space on our MD300i and despite weeks of working with Dell Tech support, we were unable to successfully add a MD1000 expansion shelf. Long story short, the MD3000i has issues and we are replacing with the MD3220. We placed the MD3220i into production on Friday afternoon (I know, I know .... never do a major upgrade on Friday ..) and it seemed to be working well with our vSphere ESXi 4.1 host server. The ESX 4.0 host server however was another matter altogether. Strange behavior, inconsistent connections, unreliable data writes, etc. After some trial and error and a nice 2 hour session with VMWare support, we uncovered the fact that the MD3220i DOES NOT support ESX 4.0. Okay ... so we begin the arduous task of migrating the VMs to the ESXi 4.1 host so that we can then migrate the data from the MD3000i SAN to the new MD3220i SAN (since the ESX 4.0 server can't reliably read/write to/from the new MD3220i, we had to migrate vms to the ESXi 4.1 host first). This seemed to go alright, except performance was noticably  slow, then got progressively slower until this morning when everything seemed to just "stop". No vCenter server available, vms sometimes available, sometimes not, extremely slow performance when you could connect to them, etc, etc. Another 3 hour support session with VMWare tech support and the tech guy uncovers errors relating to locked LUNs on the MD3220i. One of us on the con call comes up with what turns out to be a brilliant idea; shut down the ESX 4.0 host, since it is the only possible system that could be locking the MD3220i LUNs. Even though the ESX 4.0 host is properly configured as a host group member on the MD3220i and has no active vms with data traffic on any of the SANS, it still had the iSCSI Initiator and port groups active for access to the MD3220i. Sure enough, as soon as the ESX 4.0 host powers off, everything springs back to life on the ESXi 4.1 host and the lock errors cease. So here is my question (finally!): Is this problem strictly the result of the unsupported ESX 4.0 host having access to the MD3220i or is there perhaps a bug with the MD3220i that does not properly support multiple host access? I'm just asking as I'd like to know if this is a known issue before I rebuild the old ESX 4.0 host asa a ESXi 4.1 host and bring it online. If anyone has any additional insight into this, it would be great to hear from you.
MD3220i and Volume Lock Contention when ESX 4.0 and ESXi 4.1 Hosts Share 
Volumes?