System information

Setting LUN Allocations
This topic provides some general information on how to allocate LUNs when your ESX/ESXi works in
conjunction with SAN.
When you set LUN allocations, note the following points:
Storage provisioning.
To ensure that the ESX/ESXi system recognizes the LUNs at startup time,
provision all LUNs to the appropriate HBAs before you connect the SAN to the
ESX/ESXi system.
VMware recommends that you provision all LUNs to all ESX/ESXi HBAs at the
same time. HBA failover works only if all HBAs see the same LUNs.
VMotion and VMware
DRS
When you use vCenter Server and VMotion or DRS, make sure that the LUNs
for the virtual machines are provisioned to all ESX/ESXi hosts. This provides
the greatest freedom in moving virtual machines.
Active/active compared
to active/passive arrays
When you use VMotion or DRS with an active/passive SAN storage device,
make sure that all ESX/ESXi systems have consistent paths to all storage
processors. Not doing so can cause path thrashing when a VMotion migration
occurs.
For active/passive storage arrays not listed in the Storage/SAN Compatibility
Guide, VMware does not support storage port failover. In those cases, you must
connect the server to the active port on the storage array. This configuration
ensures that the LUNs are presented to the ESX/ESXi host.
Setting Fibre Channel HBA
This topic provides general guidelines for setting a FC HBA on your ESX/ESXi host.
During FC HBA setup, consider the following issues.
HBA Default Settings
FC HBAs work correctly with the default configuration settings. Follow the configuration guidelines given by
your storage array vendor.
NOTE You should not mix FC HBAs from different vendors in a single server. Having different models of the
same HBA is supported, but a single LUN can not be accessed through two different HBA types, only through
the same type. Ensure that the firmware level on each HBA is the same.
Static Load Balancing Across HBAs
With both active/active and active/passive storage arrays, you can set up your host to use different paths to
different LUNs so that your adapters are being used evenly. See “Path Management and Manual, or Static,
Load Balancing,” on page 63.
Setting the Timeout for Failover
Set the timeout value for detecting when a path fails in the HBA driver. VMware recommends that you set the
timeout to 10 seconds to ensure optimal performance.
Dedicated Adapter for Tape Drives
For best results, use a dedicated SCSI adapter for any tape drives that you are connecting to an ESX/ESXi
system. FC connected tape drives are not supported. Use the Consolidated Backup proxy, as discussed in the
Virtual Machine Backup Guide.
Fibre Channel SAN Configuration Guide
30 VMware, Inc.