During setting up an iSCSI LUN on my new Synology box (DSM 4.3), I encountered an issue where the first ESXi box would connect successfully to the iSCSI target, but not the second. So no devices showing on the second node after configuring the iSCSI adapter, despite no apparent errors during the config process.
Looking at the Synology box showed the first ESXi node connected (172.20.0.210), but not the second.
I noticed on the above screen Multiple Sessions - Disabled. I hadn’t seen any mention of that while setting up the iSCSI LUN so looked into the config.
So it appears that multiple sessions are disabled by default, accompanied by a warning that your OS must be cluster aware. Comfortable that ESXi meets that requirement, I decided to proceed.
Multiple sessions are now available.
Rescanning the iSCSI hba and the device now appears.
Now the Synology box shows multiple sessions connected.