Dell EMC Metro node 7.0.1 Administrator Guide

Enabling/disabling CAW

VMware servers discover whether the CAW SCSI command is supported:

• During initial storage scanning
• When the VMFS3.HardwareAcceleratedLocking value on the ESX host is enabled (or toggled if it is enabled)

If CAW is not supported or support is disabled, metro node returns CHECK CONDITION, ILLEGAL REQUEST, and INVALID OP-CODE. The ESX server reverts to using SCSI RESERVE and the virtual machine operation continues.

Virtual machine operations may experience significant performance degradation if CAW is not enabled.

Metro node enables CAW to be enabled/disabled for all storage associated with metro node, using a single command. When CAW is disabled on metro node, storage volumes, do not include CAW support information in their responses to inquiries from hosts.

To mark storage CAW as disabled:

• VMFS3.HardwareAcceleratedLocking must be toggled, or
• Hosts may need to rescan their storage.
  CAUTION:Enabling/disabling CAW functionality supports exceptional situations such as assisting Dell EMC Technical Support personnel to diagnose a problem. CAW is enabled by default and should be disabled only by Dell EMC Technical Support.

Support for CAW can be enabled or disabled at two levels:

• Storage view - Enabled or disabled for all existing storage views. A storage view created after CAW is enabled/disabled at the storage view level inherits the system default setting. Dell EMC recommends maintaining uniform CAW setting on all storage views. If CAW must be disabled for a given storage view, it must be disabled for all existing and future storage views. To ensure that future storage views to reflect the new setting, change the system default (described below).
• System default - Enabled or disabled as a system default. A storage view created after CAW is enabled/disabled at the system default level inherits the system default setting. If the system default is enabled, CAW support for the new storage view is also enabled.