SSD not available to add as backing for VMware vSphere Flash Read Cache

Products

VMware vCenter Server VMware vSphere ESXi

Issue/Introduction

Symptoms:

When you attempt to add a local Solid State Drive (SSD) as backing for vSphere Flash Read Cache, the drive is not available to add.
The SSD is recognized by the ESXi host but is not available to add as backing for Flash Read Cache.

Environment

VMware vCenter Server 5.5.x
VMware vSphere ESXi 5.5

Cause

This issue occurs when some local RAID controllers present volumes in a way that when claimed, they are not claimed with VMW_SATP_LOCAL. In addition, many RAID controllers do not support direct pass-through of drives.

Resolution

Notes:

Enterprise Plus Licensing is required to be able to use vSphere Flash Read Cache.

Depending on the RAID controller, it may be necessary to create a volume within the controller BIOS for the SSD (for some controllers, you must create a a single-drive RAID 0 volume) so the drive is recognized by the ESXi Host. This is not necessary for RAID controllers which support pass-through.
Some SSDs configured in the controller for RAID 0 causes problems with vSphere Flash Read Cache, such controllers should be configured to Enable HBA Mode to use the SSDs for vSphere Flash Cache. When running the esxcli storage core device list status command, you may see status entries similar to: status: degraded.

Where a customer claim rule is required, you can resolve this issue by adding one for the SSD. Verify that the SSD has the wrong claim rule by clicking on the device in the vCenter Server storage view and check in the information panel in which Storage Array Type Plugin (SATP) has claimed the device. If this is not VMW_SATP_LOCAL, you need to add a a custom claim rule.

To add a custom claim rule, perform these steps:

Open an SSH session to the affected ESXi host.
Log in as the root user.
Determine the Network Address Authority (naa) identifier of the SSD by running the command:

esxcfg-scsidevs -l | less
Scroll to the SSD device and copy the naa identifier.
To add a rule with the VMW_SATP_LOCAL SATP, run the command:

esxcli storage nmp satp rule add --satp VMW_SATP_LOCAL --device naa.XXXXXX --option enable_local

Where naa.XXXXXX is the naa ID copied in step 4.
and --option enable_local tags the device as local.
Reclaim the device by running the commands:

# esxcli storage core claimrule load
# esxcli storage core claiming reclaim -d naa.XXXXXXX

Where naa.XXXXXX is the naa ID of the SSD device.

# esxcli storage core claimrule run
In the vSphere Web Client, rescan for storage and check the SATP in the device properties to ensure it is now listed as VMW_SATP_LOCAL. If not, repeat the steps.

If using the local SATP, add the device in the vFlash Read Cache device backing dialogue box. The device is now listed and can be added successfully.

Additional Information

For more information on esxcli storage commands, see Managing NMP with esxcli storage nmp in the vSphere 5.5 Command-Line Interface Documentation Guide.