I was asked on Twitter (http://twitter.com/Rattacasa) what I've found to be the most common things overlooked when customers configure iSCSI connectivity for their VMware environments, and how they can be addressed . Here they are:

1. Read the iSCSI SAN Configuration guide from VMware (<a href="http://www.vmware.com/pdf/vsphere4/r41/vsp_41_iscsi_san_cfg.pdf" target="_blank">http://www.vmware.com/pdf/vsphere4/r41/vsp_41_iscsi_san_cfg.pdf</a>)

2. Read your storage vendor's specific VMware implementation documentation!

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3. Remember to bind your VMkernel interfaces to the iSCSI adapters (page 41. in iSCSI SAN config guide)

4. If you plan to use Jumbo Frames, make sure you enable it on the vSwitch &amp; VMkernel interfaces as well as the upstream physical switch (or physical switch interfaces, depending on make/model). (page 42 in iSCSI SAN CFG Guide).

5. If you're going to use a single vSwitch with multiple physical NICs, make sure you override the vSwitch load balancing settings for each VMk and keep a 1:1 mapping between VMkernel intefaces and physical NICs (page 38). It's generally simpler to use a separate vSwitch with a single physical NIC and a single VMk for each dedicated iSCSI connection, but some prefer less vSwitches.

6. Verify, verify, verify! Nothing like finding a speed/duplex mismatch when everything was done correctly-- but never verified!

The most important one above that seemingly resolves most of the others is #1-- read the iSCSI SAN configuration guide. Loads of valuable information in there, and while it is a bit technical, it's not overly complicated or hard to follow.