You can aggregate local flash devices on an ESXi host into a single virtualized caching layer called virtual flash resource. When you set up the virtual flash resource, you create a new file system, Virtual Flash File System (VFFS). VFFS is a derivative of VMFS, which is optimized for flash devices and is used to group the physical flash devices into a single caching resource pool. As a non-persistent resource, it cannot be used to store virtual machines.

After you set up the virtual flash resource, you can use it for I/O caching filters. See Filtering Virtual Machine I/O in vSphere.

Considerations for Virtual Flash Resource

When you configure a virtual flash resource, several considerations apply.

  • You can have only one virtual flash resource on a single ESXi host. The virtual flash resource is managed at the host's level.
  • You cannot use the virtual flash resource to store virtual machines. Virtual flash resource is a caching layer only.
  • You can use only local flash devices for the virtual flash resource.
  • You can create the virtual flash resource from mixed flash devices. All device types are treated equally and no distinction is made between SAS, SATA, or PCI express connectivity. When creating the resource from mixed flash devices, make sure to group similar performing devices together to maximize performance.
  • You cannot use the same flash devices for the virtual flash resource and vSAN. Each requires its own exclusive and dedicated flash device.

Set Up Virtual Flash Resource

You can set up a virtual flash resource or add capacity to existing virtual flash resource.

To set up a virtual flash resource, you use local flash devices connected to your host or host cluster. To increase the capacity of your virtual flash resource, you can add more devices, up to the maximum number indicated in the Configuration Maximums documentation. An individual flash device must be exclusively allocated to the virtual flash resource. No other vSphere functionality, such as vSAN or VMFS, can share the device with the virtual flash resource.

Procedure

  1. In the vSphere Client, navigate to the ESXi host.
  2. Click the Configure tab.
  3. Under Virtual Flash, click Virtual Flash Resource Management.
  4. Click one of the following options.
    Option Description
    Add Capacity If you are creating the virtual flash resource on an individual host.
    Add Capacity on Cluster If you are creating the virtual flash resource on a cluster.
  5. From the list of available entities, select one or more to use for the virtual flash resource and click OK.
    If your flash devices do not appear on the list, see Marking Storage Devices on ESXi Hosts.
    Option Description
    Local VMware Disk Select any combination of unclaimed flash devices.

    ESXi creates the VFFS volume on one of the devices and then extends the volume on the rest of the devices. The system configures the virtual flash resource on the entire VFFS volume.

    If a VFFS volume exists on your host, you cannot select any unclaimed devices without first selecting the existing VFFS volume.

    volume ID - Configure using the existing VFFS volume extents

    If you previously created a VFFS volume on one of the host's flash devices using the vmkfstools command, the volume also appears on the list of eligible entities. You can select just this volume for the virtual flash resource. Or combine it with the unclaimed devices. ESXi uses the existing VFFS volume to extend it over other devices.

Results

The virtual flash resource is created. The Device Backing area lists all devices that you use for the virtual flash resource.

What to do next

Use the virtual flash resource for I/O caching filters developed through vSphere APIs for I/O Filtering. See Using Cache I/O Filters with Flash Storage Devices on ESXi Hosts.

You can increase the capacity by adding more flash devices to the virtual flash resource.

Remove Virtual Flash Resource

You might need to remove a virtual flash resource deployed on local flash devices connected to the ESXi host. Removing the virtual flash resource frees the devices for other services.

Prerequisites

  • Verify that the virtual flash resource is not used for I/O filters.

Procedure

  1. In the vSphere Client, navigate to the ESXi host.
  2. Click the Configure tab.
  3. Under Virtual Flash, click Virtual Flash Resource Management and click Remove All.

Results

After you remove the virtual flash resource and erase the flash device, the device is available for other operations.

Set Alarm for Virtual Flash Use

Set an alarm to indicate when the use of a virtual flash resource on your ESXi host exceeds specified threshold.

Procedure

  1. In the vSphere Client, navigate to the ESXi host.
  2. Click the Configure tab.
  3. Under System, click Advanced System Settings.
  4. Select the setting to change and click the Edit button.
    Parameter Description
    VFLASH.ResourceUsageThreshold The system triggers the Host vFlash resource usage alarm when a virtual flash resource use exceeds the threshold. The default threshold is 80%. You can change the threshold to an appropriate value. The alarm is cleared when the virtual flash resource use drops below the threshold.
  5. Click OK.