Be careful of that host mode
Host connectivity is sometimes misinterpreted or ignored when it comes to virtualized servers. Many vendors are trying to address this. For example, some of the newer arrays now contain a "VMware" mode to be set only if you're running VMware ESX Server. If the arrays in your environment don't have such a mode, please check with your vendor to learn the recommended settings. Care should be taken to ensure that specific settings such as SCSI reservations to implement clustered hypervisors are set in advance to prevent any hiccups during failover.
Keep in mind that standard multipathing software may not work on hypervisors or virtual systems in the same manner it works on standard operating platforms. Some virtualization vendors bundle their own path management software, which eliminates the need for a third-party add-on.
Virtualization and iPod revolutions
A parallel could be drawn between virtualization and the iPod. For every iPod sold, there are plenty of auxiliary technologies sold (from docking stations to boom boxes) that are designed to make the experience better. Virtualization appears to be headed that way.
One technology I'd like to highlight is N_Port ID Virtualization (NPIV). It's fairly new and was created by IBM with virtualization on its System z9. NPIV allows a single FC port to register more than one World Wide Port Name (WWPN) with a fabric name server. Each registered WWPN is thus assigned a unique N_Port ID. With NPIV, a single physical HBA port can appear as multiple WWPNs in the FC fabric. It also lets you create and map a WWPN for each virtual server. Therefore, from a LUN masking perspective, each virtual server can have a set of unique LUNs on the same storage port. Most major virtualization vendors support it.
Remember, virtualization is your friend and it's here to stay. It's prudent to embrace it now, and in the right way, so the benefits aren't felt by just the systems and applications teams but also by the storage crew.
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