System information

Figure 2-1. Sharing a VMFS Datastore Across ESX/ESXi Hosts

VMFS volume

ESX/ESXi

virtual

disk

files

VM1 VM2 VM3

disk1

disk2

disk3

Because virtual machines share a common VMFS datastore, it might be difficult to characterize peak-access

periods or to optimize performance. You must plan virtual machine storage access for peak periods, but

different applications might have different peak-access periods. VMware recommends that you load balance

virtual machines over servers, CPU, and storage. Run a mix of virtual machines on each server so that not all

experience high demand in the same area at the same time.

Metadata Updates

A VMFS datastore holds virtual machine files, directories, symbolic links, RDMs, and so on. A VMS 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 the attributes of a virtual machine file are accessed or modified when, for

example, you perform one of the following operations:

Creating, growing, or locking a virtual machine file

Changing a file's attributes

Powering a virtual machine on or off

Making LUN Decisions

You must plan how to set up storage for your ESX/ESXi systems before you format LUNs with VMFS

datastores.

When you make your LUN decision, keep in mind the following considerations:

Each LUN should have the correct RAID level and storage characteristic for applications in virtual

machines that use it.

One LUN must contain only one VMFS datastore.

If multiple virtual machines access the same VMFS, use disk shares to prioritize virtual machines.

You might want fewer, larger LUNs for the following reasons:

More flexibility to create virtual machines without asking the storage administrator for more space.

More flexibility for resizing virtual disks, doing snapshots, and so on.

Fewer VMFS datastores to manage.

Chapter 2 Using ESX/ESXi with Fibre Channel SAN

VMware, Inc. 19