6.0.1

Table Of Contents
VMkernel and Storage 22
The VMkernel is a high-performance operating system that runs directly on the ESXi host. The VMkernel
manages most of the physical resources on the hardware, including memory, physical processors, storage,
and networking controllers.
To manage storage, VMkernel has a storage subsystem that supports several Host Bus Adapters (HBAs)
including parallel SCSI, SAS, Fibre Channel, FCoE, and iSCSI. These HBAs connect a wide variety of active-
active, active-passive, and ALUA storage arrays that are certied for use with the VMkernel. See the vSphere
Compatibility Guide for a list of the supported HBAs and storage arrays.
The primary le system that the VMkernel uses is the VMware Virtual Machine File System (VMFS). VMFS
is a cluster le system designed and optimized to support large les such as virtual disks and swap les.
The VMkernel also supports the storage of virtual disks on NFS le systems.
The storage I/O path provides virtual machines with access to storage devices through device emulation.
This device emulation allows a virtual machine to access les on a VMFS or NFS le system as if they were
SCSI devices. The VMkernel provides storage virtualization functions such as the scheduling of I/O requests
from multiple virtual machines and multipathing.
In addition, VMkernel oers several Storage APIs that enable storage partners to integrate and optimize
their products for vSphere.
The following graphic illustrates the basics of the VMkernel core, with special aention to the storage stack.
Storage-related modules reside between the logical device I/O scheduler and the adapter I/O scheduler
layers.
VMware, Inc.
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