During a recent install of a three-host ESXi cluster with an EqualLogic PS6000XV and redundant, dedicated iSCSI switches I noticed a peculiar issue with the number of paths to SAN volumes each server reported. The hosts had four ports allocated to iSCSI traffic, and all vmkernel connections were properly configured. The configuration on the switches was also correct, but I was only seeing two paths from each server to each of the six volumes instead of four. After a rescan, additional paths would briefly appear as “dead” and then drop back to 12 for all volumes.

The solution to the problem is within the default configuration of the Multipath Extension Module (MEM), which limits the number of connections to each member to two and the total volume sessions to 6, by default. The MEM configuration guide describes this, but it has been awhile since I’ve read through the entire thing.

“The default EHCM behavior is to create two sessions per volume slice, with a maximum of six sessions per volume. However, you can alter this behavior (see EHCM Configuration File). “

The EqualLogic Host Connection Manager configuration file (echmd.conf) resides in /etc/cim/dell/ and looks like this:

# EHCM configuration file
reconfig:240
upload:120
totalsessions:512
volumesessions:6
membersessions:2

I modified the file to:

# EHCM configuration file
reconfig:240
upload:120
totalsessions:512
volumesessions:12
membersessions:4

Once completed on all hosts, I rebooted them and verified all 24 paths from each host (4 paths to 6 volumes) were visible and alive.