While installing a new iSCSI SAN to host our new VMware environment I ran into an issue that took me a while to figure out and I thought that I would pass is along.
Our setup is a 10GbE iSCSI connected SAN being backed up by a Windows 2008 R2 Netbackup Enterprise Server 7.5.0.6 to a 4Gbps FC-attached LTO3 tape library. I had already set up the zoning on the FC side and had configured vCenter and the VMware hosts (5.1) so that I could see the datastores and build VMs, etc. However, every time I try to run a backup I got the following error:
ERR - Error opening the snapshot disks using given transport mode: Status 23
Perplexed, I went digging through the SAN with our SAN architect and realized that I had forgotten to add the IQN of the Netbackup Master server (master and media are the same in our environment). This didn't help and the backups errored with the same message.
I went back to the Netbackup Master Server and opened up the iSCSI initiators (Start > Administrative Tools > iSCSI Initiators) and realized that I couldn't see the SAN from the Netbackup Master Server. I grabbed the IP address of the SAN and iSCSI Initiator Properties > Targets > and did a quick connect. The 2 paths were discovered and I clicked connect and we were off to the races.
Not a huge thing, but lots of article suggest that this is a DNS name resolution issue and I wanted to point out that sometimes you've got to look a little deeper to find the problem.
Cheers,
Josh