System information

Disable Sparse LUN Support
You can disable the default sparse LUN support to decrease the time ESX/ESXi needs to scan for LUNs.
The VMkernel provides sparse LUN support by default. The sparse LUN support enables the VMkernel to
perform uninterrupted LUN scanning when a storage system presents LUNs with nonsequential LUN
numbering, for example 0, 6, and 23. If all LUNs that your storage system presents are sequential, you can
disable the sparse LUN support.
Procedure
1 In the vSphere Client inventory panel, select the host, click the Configuration tab, and click Advanced
Settings.
2 In the Advanced Settings dialog box, select Disk.
3 Scroll down to Disk.SupportSparseLUN, change the value to 0, and click OK.
N-Port ID Virtualization
N-Port ID Virtualization (NPIV) is an ANSI T11 standard that describes how a single Fibre Channel HBA port
can register with the fabric using several worldwide port names (WWPNs). This allows a fabric-attached N-
port to claim multiple fabric addresses. Each address appears as a unique entity on the Fibre Channel fabric.
How NPIV-Based LUN Access Works
NPIV enables a single FC HBA port to register several unique WWNs with the fabric, each of which can be
assigned to an individual virtual machine.
SAN objects, such as switches, HBAs, storage devices, or virtual machines can be assigned World Wide Name
(WWN) identifiers. WWNs uniquely identify such objects in the Fibre Channel fabric. When virtual machines
have WWN assignments, they use them for all RDM traffic, so the LUNs pointed to by any of the RDMs on
the virtual machine must not be masked against its WWNs. When virtual machines do not have WWN
assignments, they access storage LUNs with the WWNs of their host’s physical HBAs. By using NPIV, however,
a SAN administrator can monitor and route storage access on a per virtual machine basis. The following section
describes how this works.
When a virtual machine has a WWN assigned to it, the virtual machine’s configuration file (.vmx) is updated
to include a WWN pair (consisting of a World Wide Port Name, WWPN, and a World Wide Node Name,
WWNN). As that virtual machine is powered on, the VMkernel instantiates a virtual port (VPORT) on the
physical HBA which is used to access the LUN. The VPORT is a virtual HBA that appears to the FC fabric as
a physical HBA, that is, it has its own unique identifier, the WWN pair that was assigned to the virtual machine.
Each VPORT is specific to the virtual machine, and the VPORT is destroyed on the host and it no longer appears
to the FC fabric when the virtual machine is powered off. When a virtual machine is migrated from one ESX/
ESXi to another, the VPORT is closed on the first host and opened on the destination host.
If NPIV is enabled, four WWN pairs (WWPN & WWNN) are specified for each virtual machine at creation
time.When a virtual machine using NPIV is powered on, it uses each of these WWN pairs in sequence to try
to discover an access path to the storage. The number of VPORTs that are instantiated equals the number of
physical HBAs present on the host up to the maximum of four. A VPORT is created on each physical HBA that
a physical path is found on. Each physical path is used to determine the virtual path that will be used to access
the LUN.Note that HBAs that are not NPIV-aware are skipped in this discovery process because VPORTs
cannot be instantiated on them.
NOTE If a host has four physical HBAs as paths to the storage, all physical paths must be zoned to the virtual
machine by the SAN administrator. This is required to support multipathing even though only one path at a
time will be active.
Chapter 6 Managing ESX/ESXi Systems That Use SAN Storage
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