We've recently migrated from FC to iSCSI 10Gbps on an EMC Unity 350F Storage.
Active controller on EMC is connected to 2 switches with different VLANs per port (access). Hypervisor nodes are connected to the two switches with bonding (active-backup). We run vlan trunks 802.1q on top. Multipathd works on top of this. We run oVirt (RHEV) for virtualization.
I have problems booting VMs with IDE disks. VM takes very long after BIOS to scan and boot from disk. Both IDE/virtio disks take long mounting /boot on boot. It seems than scanning disk takes very long.
If I disable the second (active SP) controller port (or logout from it) then everything works fine. After boot, access to storage is also fine no matter if I have multipath or not.
The problem seems to be some kind of scanning on disk.
I have no errors on network interfaces or on the switches.