ATS-Only Mechanism

For storage devices that support T10 standard-based VAAI specifications, VMFS provides ATS locking, also called hardware-assisted locking. The ATS algorithm supports discrete locking per disk sector. All newly formatted VMFS5 and VMFS6 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 filters out non-ATS devices. This filtering allows you to use only those devices that support the ATS primitive.

In certain cases, you might need to turn off the ATS-only setting for a VMFS5 or VMFS6 datastore.

ATS+SCSI Mechanism

A VMFS datastore that supports the ATS+SCSI mechanism is configured to use ATS and attempts 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 or VMFS6 datastores on storage devices that do not support ATS use the ATS+SCSI mechanism.

Change Locking Mechanism to ATS+SCSI

When you create a VMFS5 datastore on a device that supports the atomic test and set (ATS) locking, the datastore uses the ATS-only locking mechanism. In certain circumstances, you might need to downgrade the ATS-only locking to ATS+SCSI.

You might need to switch to the ATS+SCSI locking mechanism when, for example, your storage device is downgraded. Or when firmware updates fail and the device no longer supports ATS.

The downgrade process is similar to the ATS-only upgrade. As with the upgrade, depending on your storage configuration, you can perform the downgrade in online or offline mode.

Procedure

  1. Change the locking mechanism to ATS+SCSI by running the following command:

    esxcli storage vmfs lockmode set -s|–scsi -l|–volume-label= VMFS label -u|–volume-uuid= VMFS UUID.

  2. For an online mode, close the datastore on all hosts that have access to the datastore, so that the hosts can recognize the change.

Change VMFS Locking to ATS-Only

If your VMFS datastore uses the ATS+SCSI locking mechanism, you can change to ATS-only locking.

Typically, VMFS5 datastores that were previously upgraded from VMFS3 continue using the ATS+SCSI locking mechanism. If the datastores are deployed on ATS-enabled hardware, they are eligible for an upgrade to ATS-only locking. Depending on your vSphere environment, you can use one of the following upgrade modes:

  • The online upgrade to the ATS-only mechanism is available for most single-extent VMFS5 datastores. While you perform the online upgrade on one of the hosts, other hosts can continue using the datastore.

  • The offline upgrade to ATS-only must be used for VMFS5 datastores that span multiple physical extents. Datastores composed of multiple extents are not eligible for the online upgrade. These datastores require that no hosts actively use the datastores at the time of the upgrade request.

Procedure:

You must perform several steps to prepare your environment for an online or offline upgrade to ATS-only locking.

Procedure

  1. Upgrade all hosts that access the VMFS5 datastore to the newest version of vSphere.
  2. Determine whether the datastore is eligible for an upgrade of its current locking mechanism by running the esxcli storage vmfs lockmode listcommand.

    The following sample output indicates that the datastore is eligible for an upgrade. It also shows the current locking mechanism and the upgrade mode available for the datastore.

    Locking Mode             ATS Compatible                ATS Upgrade Modes
    ————                    ————–                         —————–
    ATS+SCSI                   true                                       Online or Offline
  3. Depending on the upgrade mode available for the datastore, perform one of the following actions:

    Upgrade Mode

    Action

    Online

    Verify that all hosts have consistent storage connectivity to the VMFS datastore.

    Offline

    Verify that no hosts are actively using the datastore.

Upgrade Locking Mechanism to the ATS-Only Type

If a VMFS datastore is ATS-only compatible, you can upgrade its locking mechanism from ATS+SCSI to ATS-only.

Most datastores that do not span multiple extents are eligible for an online upgrade. While you perform the online upgrade on one of the ESXi hosts, other hosts can continue using the datastore. The online upgrade completes only after all hosts have closed the datastore.

Prerequisites

If you plan to complete the upgrade of the locking mechanism by putting the datastore into maintenance mode, disable Storage DRS. This prerequisite applies only to an online upgrade.

Procedure

  1. Perform an upgrade of the locking mechanism by running the following command:

    esxcli storage vmfs lockmode set -a|–ats -l|–volume-label= VMFS label -u|–volume-uuid= VMFS UUID.

  2. For an online upgrade, perform additional steps.
    1. Close the datastore on all hosts that have access to the datastore, so that the hosts can recognize the change.

      You can use one of the following methods:

      • Unmount and mount the datastore.

      • Put the datastore into maintenance mode and exit maintenance mode.

    2. Verify that the Locking Mode status for the datastore changed to ATS-only by running:

      esxcli storage vmfs lockmode list

    3. If the Locking Mode displays any other status, for example ATS UPGRADE PENDING, check which host has not yet processed the upgrade by running:

      esxcli storage vmfs host list