Qlogic Fibre Channel HBA and VM Informations techniques Page 19

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Figure 2-1. Sharing a VMFS Datastore Across ESX/ESXi Hosts
VMFS volume
ESX/ESXi
A
ESX/ESXi
B
ESX/ESXi
C
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:
n
Creating, growing, or locking a virtual machine file
n
Changing a file's attributes
n
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:
n
Each LUN should have the correct RAID level and storage characteristic for applications in virtual
machines that use it.
n
One LUN must contain only one VMFS datastore.
n
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:
n
More flexibility to create virtual machines without asking the storage administrator for more space.
n
More flexibility for resizing virtual disks, doing snapshots, and so on.
n
Fewer VMFS datastores to manage.
Chapter 2 Using ESX/ESXi with Fibre Channel SAN
VMware, Inc. 19
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