Virtual Flash caching is not working

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VMware vCenter Server VMware vSphere ESXi

Symptoms:

You have configured a virtual machine with Virtual Flash Read Cache and you experience these symptoms:

VMware vCenter Server 5.5.x
VMware vSphere ESXi 5.5

To troubleshoot this issue, verify if:

The Virtual Flash cache resource is configured correctly. For more information, see Setting up a Virtual Flash resource in vSphere 5.5 (2051647).
The cache had sufficient time to build. It can take quite some time for the Virtual Flash cache to build.
The virtual machine was migrated recently. If yes, check if the Always migrate the cache contents option is selected in the Select Virtual Flash Read Cache Migration Settings. For more information, see Migrating virtual machines with Virtual Flash (2051645).
Sufficient Virtual Flash cache resource is granted to the virtual machine.

To verify this, select the virtual machine, click Edit Settings > Hard disk > Virtual Flash Read Cache, and check if the value greater than 0.
The advanced option Advanced > Block size is set to a block size that matches the majority of I/O the virtual machine’s workload. For more information, see Adjusting the amount of Virtual Flash Read Cache resources assigned to a virtual machine (2057829).
All available Virtual Flash resources are configured as Host Swap Cache. For more information, see Configuring Host Swap Cache with Virtual Flash Read Cache resources (2059285).

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