vSphere Storage - ESXi 5.1 - Documentation - VMware
vSphere Storage - ESXi 5.1 - Documentation - VMware
vSphere Storage - ESXi 5.1 - Documentation - VMware
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<strong>vSphere</strong> <strong>Storage</strong><br />
Sharing a VMFS Datastore Across Hosts<br />
As a cluster file system, VMFS lets multiple <strong>ESXi</strong> hosts access the same VMFS datastore concurrently. You can<br />
connect up to 128 hosts to a single VMFS datastore.<br />
Figure 17-1. Sharing a VMFS Datastore Across Hosts<br />
host<br />
A<br />
host<br />
B<br />
VMFS volume<br />
virtual<br />
disk<br />
files<br />
host<br />
C<br />
VM1 VM2 VM3<br />
disk1<br />
disk2<br />
disk3<br />
To ensure that the same virtual machine is not accessed by multiple servers at the same time, VMFS provides<br />
on-disk locking.<br />
Sharing the same VMFS volume across multiple hosts offers the following advantages:<br />
n You can use <strong>VMware</strong> Distributed Resource Scheduling (DRS) and <strong>VMware</strong> High Availability (HA).<br />
You can distribute virtual machines across different physical servers. That means you run a mix of virtual<br />
machines on each server so that not all experience high demand in the same area at the same time. If a<br />
server fails, you can restart virtual machines on another physical server. In case of a failure, the on-disk<br />
lock for each virtual machine is released. For more information about <strong>VMware</strong> DRS, see the <strong>vSphere</strong><br />
Resource Management documentation. For information about <strong>VMware</strong> HA, see the <strong>vSphere</strong> Availability<br />
documentation.<br />
n You can use vMotion to migrate running virtual machines from one physical server to another. To support<br />
vMotion between <strong>ESXi</strong> 5 and version 3.x or 4.x hosts, virtual machines must be located on VMFS3 volumes.<br />
For information about migrating virtual machines, see the vCenter Server and Host Management<br />
documentation.<br />
VMFS Metadata Updates<br />
A VMFS datastore holds virtual machine files, directories, symbolic links, RDM descriptor files, and so on. The<br />
datastore also maintains a consistent view of all the mapping information for these objects. This mapping<br />
information is called metadata.<br />
Metadata is updated each time you perform datastore or virtual machine management operations. Examples<br />
of operations requiring metadata updates include the following:<br />
n Creating, growing, or locking a virtual machine file<br />
n Changing a file's attributes<br />
n Powering a virtual machine on or off<br />
n Creating or deleting a VMFS datastore<br />
n Expanding a VMFS datastore<br />
156 <strong>VMware</strong>, Inc.