vSphere Storage - ESXi 5.1 - Documentation - VMware

With ESXi hosts, use a single-initiator zoning or a single-initiator-single-target zoning. The latter is a preferred
zoning practice. Using the more restrictive zoning prevents problems and misconfigurations that can occur on
the SAN.
For detailed instructions and best zoning practices, contact storage array or switch vendors.
How Virtual Machines Access Data on a Fibre Channel SAN
ESXi stores a virtual machine's disk files within a VMFS datastore that resides on a SAN storage device. When
virtual machine guest operating systems issue SCSI commands to their virtual disks, the SCSI virtualization
layer translates these commands to VMFS file operations.
When a virtual machine interacts with its virtual disk stored on a SAN, the following process takes place:
1 When the guest operating system in a virtual machine reads or writes to a SCSI disk, it issues SCSI
commands to the virtual disk.
2 Device drivers in the virtual machine’s operating system communicate with the virtual SCSI controllers.
3 The virtual SCSI controller forwards the command to the VMkernel.
4 The VMkernel performs the following tasks.
a Locates the file in the VMFS volume that corresponds to the guest virtual machine disk.
b Maps the requests for the blocks on the virtual disk to blocks on the appropriate physical device.
c Sends the modified I/O request from the device driver in the VMkernel to the physical HBA.
5 The physical HBA performs the following tasks.
a Packages the I/O request according to the rules of the FC protocol.
b Transmits the request to the SAN.
Chapter 3 Using ESXi with Fibre Channel SAN
6 Depending on a port the HBA uses to connect to the fabric, one of the SAN switches receives the request
and routes it to the storage device that the host wants to access.
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