6.0.1

Table Of Contents
When you run multiple virtual machines, VMFS provides specic locking mechanisms for virtual machine
les, so that virtual machines can operate safely in a SAN environment where multiple ESXi hosts share the
same VMFS datastore.
In addition to virtual machines, the VMFS datastores can store other les, such as virtual machine templates
and ISO images.
Sharing a VMFS Datastore Across Hosts
As a cluster le system, VMFS lets multiple ESXi hosts access the same VMFS datastore concurrently.
Figure 161. Sharing a VMFS Datastore Across Hosts
VMFS volume
host
A
host
B
host
C
virtual
disk
files
VM1 VM2 VM3
disk1
disk2
disk3
For information on the maximum number of hosts that can connect to a single VMFS datastore, see the
Conguration Maximums document.
To ensure that the same virtual machine is not accessed by multiple servers at the same time, VMFS
provides on-disk locking.
Sharing the same VMFS volume across multiple hosts oers the following advantages:
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You can use VMware Distributed Resource Scheduling (DRS) and VMware High Availability (HA).
You can distribute virtual machines across dierent physical servers. That means you run a mix of
virtual machines on each server so that not all experience high demand in the same area at the same
time. If a server fails, you can restart virtual machines on another physical server. In case of a failure, the
on-disk lock for each virtual machine is released. For more information about VMware DRS, see the
vSphere Resource Management documentation. For information about VMware HA, see the vSphere
Availability documentation.
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You can use vMotion to migrate running virtual machines from one physical server to another. For
information about migrating virtual machines, see the vCenter Server and Host Management
documentation.
VMFS Metadata Updates
A VMFS datastore holds virtual machine les, directories, symbolic links, RDM descriptor les, and so on.
The datastore also maintains a consistent view of all the mapping information for these objects. This
mapping information is called metadata.
Metadata is updated each time you perform datastore or virtual machine management operations. Examples
of operations requiring metadata updates include the following:
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Creating, growing, or locking a virtual machine le
vSphere Storage
148 VMware, Inc.