The hardware acceleration functionality enables the ESXi host to integrate with compliant storage systems. The host can offload certain virtual machine and storage management operations to the storage systems. With the storage hardware assistance, your host performs these operations faster and consumes less CPU, memory, and storage fabric bandwidth.

Block storage devices, Fibre Channel and iSCSI, and NAS devices support the hardware acceleration.

For additional details, see the VMware knowledge base article at http://kb.vmware.com/kb/1021976.

Hardware Acceleration Benefits

When the hardware acceleration functionality is supported, the host can get hardware assistance and perform the following tasks faster and more efficiently.

  • Migrating virtual machines with Storage vMotion
  • Deploying virtual machines from templates
  • Cloning virtual machines or templates
  • VMFS clustered locking and metadata operations for virtual machine files
  • Provisioning thick virtual disks
  • Creating fault-tolerant virtual machines
  • Creating and cloning thick disks on NFS datastores

Hardware Acceleration Requirements

The hardware acceleration functionality works only if you use an appropriate host and storage array combination.
Table 1. Hardware Acceleration Storage Requirements
ESXi Block Storage Devices NAS Devices
ESXi Support T10 SCSI standard, or block storage plug-ins for array integration (VAAI) Support NAS plug-ins for array integration
Note: If your SAN or NAS storage fabric uses an intermediate appliance in front of a storage system that supports hardware acceleration, the intermediate appliance must also support hardware acceleration and be properly certified. The intermediate appliance might be a storage virtualization appliance, I/O acceleration appliance, encryption appliance, and so on.

Hardware Acceleration Support Status

For each storage device and datastore, the vSphere Client display the hardware acceleration support status.

The status values are Unknown, Supported, and Not Supported. The initial value is Unknown.

For block devices, the status changes to Supported after the host successfully performs the offload operation. If the offload operation fails, the status changes to Not Supported. The status remains Unknown if the device provides partial hardware acceleration support.

With NAS, the status becomes Supported when the storage can perform at least one hardware offload operation.

When storage devices do not support or provide partial support for the host operations, your host reverts to its native methods to perform unsupported operations.

Hardware Acceleration Considerations

When you use the hardware acceleration functionality with ESXi, certain considerations apply.

Several reasons might cause a hardware-accelerated operation to fail.

For any primitive that the array does not implement, the array returns an error. The error triggers the ESXi host to attempt the operation using its native methods.

The VMFS data mover does not leverage hardware offloads and instead uses software data movement when one of the following occurs:

  • The source and destination VMFS datastores have different block sizes.
  • The source file type is RDM and the destination file type is non-RDM (regular file).
  • The source VMDK type is eagerzeroedthick and the destination VMDK type is thin.
  • The source or destination VMDK is in sparse or hosted format.
  • The source virtual machine has a snapshot.
  • The logical address and transfer length in the requested operation are not aligned to the minimum alignment required by the storage device. All datastores created with the vSphere Client are aligned automatically.
  • The VMFS has multiple LUNs or extents, and they are on different arrays.

Hardware cloning between arrays, even within the same VMFS datastore, does not work.