System information

You might want more, smaller LUNs for the following reasons:
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Less wasted storage space.
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Different applications might need different RAID characteristics.
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More flexibility, as the multipathing policy and disk shares are set per LUN.
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Use of Microsoft Cluster Service requires that each cluster disk resource is in its own LUN.
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Better performance because there is less contention for a single volume.
When the storage characterization for a virtual machine is not available, there is often no simple answer when
you have to decide on the LUN size and number of LUNs to use. You can experiment using either predictive
or adaptive scheme.
Use the Predictive Scheme to Make LUN Decisions
When you plan how to set up your storage for your ESX/ESXi systems before you format LUNs with VMFS
datastores, you must decide on the LUN size and number of LUNs to use. You can experiment using the
predictive scheme.
Procedure
1 Create several LUNs with different storage characteristics.
2 Build a VMFS datastore on each LUN, labeling each datastore according to its characteristics.
3 Allocate virtual disks to contain the data for virtual machine applications in the VMFS datastores built on
LUNs with the appropriate RAID level for the applications' requirements.
4 Use disk shares to distinguish high-priority from low-priority virtual machines.
Disk shares are relevant only within a given host. The shares assigned to virtual machines on one host
have no effect on virtual machines on other hosts.
5 Run the applications to determine whether virtual machine performance is acceptable.
Use the Adaptive Scheme to Make LUN Decisions
When you plan how to set up your storage for your ESX/ESXi systems before you format LUNs with VMFS
datastores, you must decide on the LUN size and number of LUNs to use. You can experiment using the
adaptive scheme.
Procedure
1 Create a large LUN (RAID 1+0 or RAID 5), with write caching enabled.
2 Build a VMFS on that LUN.
3 Place four or five virtual disks on the VMFS.
4 Run the applications to determine whether disk performance is acceptable.
If performance is acceptable, you can place additional virtual disks on the VMFS. If performance is not
acceptable, create a new, larger LUN, possibly with a different RAID level, and repeat the process. Use
migration so that you do not lose virtual machines when you recreate the LUN.
Fibre Channel SAN Configuration Guide
20 VMware, Inc.