Do major virtualization vendors assign truly unique WWNs to virtual storage?
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In theory, WWNs assigned by any of the major vendors should be unique, as those are assigned by the Institute of Electrical and Electronics Engineers, but there are a few exceptions to this rule. For unique World Wide Names (WWNs) per virtual machine, you need to have N_Port ID Virtualization (NPIV) within your virtual host environment. Nearly all modern versions of major virtualization platforms offer NPIV, but when you're not running the most recent version, you're restricted to the WWN of the physical host bus adapter (HBA). NPIV allows for virtual HBAs and thus, more WWNs per port. Virtual HBAs help ensure that each virtual server accesses only its assigned virtual storage, and many modern operating systems have begun to offer native virtual HBA support.
In practice, the virtual HBAs could very well generate the same WWN, as is often the case with MAC addresses. This does not often occur when all hosts are joined into a unified environment, however, as the virtualization management software prevents conflicts. Duplicate WWNs are possible with multiple environments, but the 128-bit namespace of WWNs is much larger than the 48-bit MAC addresses, making conflicts less likely.
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