6.0.1

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Changing a le's aributes
n
Powering a virtual machine on or o
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Creating or deleting a VMFS datastore
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Expanding a VMFS datastore
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Creating a template
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Deploying a virtual machine from a template
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Migrating a virtual machine with vMotion
When metadata changes are made in a shared storage enviroment, VMFS uses special locking mechanisms
to protect its data and prevent multiple hosts from concurrently writing to the metadata.
VMFS Locking Mechanisms
In a shared storage environment, when multiple hosts access the same VMFS datastore, specic locking
mechanisms are used. These locking mechanisms prevent multiple hosts from concurrently writing to the
metadata and ensure that no data corruption occurs.
Depending on its conguration and the type of underlying storage, a VMFS datastore can exclusively use
the atomic test and set locking mechanism (ATS-only), or use a combination of ATS and SCSI reservations
(ATS+SCSI).
ATS-Only Mechanism
For storage devices that support T10 standard-based VAAI specications, VMFS provides ATS locking, also
called hardware assisted locking. The ATS algorithm supports discrete locking per disk sector. All newly
formaed VMFS5 datastores use the ATS-only mechanism if the underlying storage supports it, and never
use SCSI reservations.
When you create a multi-extent datastore where ATS is used, vCenter Server lters out non-ATS devices.
This ltering allows you to use only those devices that support the ATS primitive.
In certain cases, you might need to turn o the ATS-only seing for a VMFS5 datastore. For information, see
“Change Locking Mechanism to ATS+SCSI,” on page 152.
ATS+SCSI Mechanism
A VMFS datastore that supports the ATS+SCSI mechanism is congured to use ATS and aempts to use it
when possible. If ATS fails, the VMFS datastore reverts to SCSI reservations. In contrast with the ATS
locking, the SCSI reservations lock an entire storage device while an operation that requires metadata
protection is performed. After the operation completes, VMFS releases the reservation and other operations
can continue.
Datastores that use the ATS+SCSI mechanism include VMFS5 datastores that were upgraded from VMFS3.
In addition, new VMFS5 datastores on storage devices that do not support ATS use the ATS+SCSI
mechanism.
If your VMFS datastore reverts to SCSI reservations, you might notice performance degradation caused by
excessive SCSI reservations. For information about how to reduce SCSI reservations, see the vSphere
Troubleshooting documentation.
Display VMFS Locking Information
Use the esxcli command to obtain information about the locking mechanism that a VMFS datastore uses.
In the procedure, --server=server_name species the target server. The specied target server prompts you
for a user name and password. Other connection options, such as a conguration le or session le, are
supported. For a list of connection options, see Geing Started with vSphere Command-Line Interfaces.
Chapter 16 Working with Datastores
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