6.5.1

Table Of Contents
Problem
Excessive SCSI reservations cause performance degradation and SCSI reservation conflicts.
Cause
Several operations require VMFS to use SCSI reservations.
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Creating, resignaturing, or expanding a VMFS datastore
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Powering on a virtual machine
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Creating or deleting a file
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Creating a template
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Deploying a virtual machine from a template
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Creating a new virtual machine
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Migrating a virtual machine with VMotion
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Growing a file, such as a thin provisioned virtual disk
Note For storage devices that support the hardware acceleration, the hosts use the atomic test and set
(ATS) algorithm to lock the LUN. For more information on hardware acceleration, see the vSphere
Storage documentation.
Solution
To eliminate potential sources of SCSI reservation conflicts, follow these guidelines:
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Serialize the operations of the shared LUNs, if possible, limit the number of operations on different
hosts that require SCSI reservation at the same time.
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Increase the number of LUNs and limit the number of hosts accessing the same LUN.
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Reduce the number snapshots. Snapshots cause numerous SCSI reservations.
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Reduce the number of virtual machines per LUN. Follow recommendations in Configuration
Maximums.
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Make sure that you have the latest HBA firmware across all hosts.
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Make sure that the host has the latest BIOS.
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Ensure a correct Host Mode setting on the SAN array.
For information about handling SCSI reservation conflicts on specific storage arrays, see the VMware
knowledge base article at http://kb.vmware.com/kb/1005009.
Path Thrashing Causes Slow LUN Access
If your ESXi host is unable to access a LUN, or access is very slow, you might have a problem with path
thrashing, also called LUN thrashing.
vSphere Troubleshooting
VMware, Inc. 64