Symptoms:
Failed to power on the virtual machine. Cannot create Flash Read Cache: Operation failed.
You might get the error related to  "The "Power on virtual machine" operation failed for the entity with the following error message. The available virtual flash resource '0' MB ('0' bytes) is not sufficient for the requested operation.

VMware vCenter Server Appliance 6.7.x
VMware vCenter Server Appliance 6.0.x
VMware vSphere Web Client 6.5.x
VMware vCenter Server Appliance 6.5.x

The SSD drive used as vFlash Read Cache (vFRC) was removed from ESXi host in which a VM has been registered and configured to use vFRC, in the absence of SSD card a power-on operation of VM will fail.

To power-on, the affected VM, perform below task,
 
Change the value from TRUE to FALSE for vFlash entry 

Before you edit the vmx file, take a backup of vmx file. 

# cp <VM>vmx <VM>.vmx.backup
 
Use vi editor to change the disk value 
# vi <VM>.vmx  
sched.scsi0:0.vFlash.enabled = "TRUE" and change to  "FALSE"

Suppose if the VM has many disks and you wanted to change the value for all the disk then use the sed command to change the value. For each vmdk file that is configured to use vFRC, there is a corresponding entry in the vmx file, that controls vFRC.

In order to turn off vFRC acceleration for a given disk, download the vmx file, and change the value for .vFlash.enabled from TRUE to FALSE

Example:
sched.scsi0:0.vFlash.enabled = "TRUE"
sched.scsi0:0.vFlash.enabled = "FALSE"
 
1. List out all the disk which has vFRC enabled

#  cat <VM>.vmx | grep -i flash.enabled
sched.scsi0:3.vFlash.enabled = "TRUE"
sched.scsi0:5.vFlash.enabled = "TRUE"
sched.scsi0:11.vFlash.enabled = "TRUE"
sched.scsi0:12.vFlash.enabled = "TRUE"

2. Take a backup of the VMX file
# cp <VM>vmx <VM>.vmx.backup

3. Use the below command to change the value from TRUE to FALSE
# sed -i 's/vFlash.enabled = "TRUE"/vFlash.enabled = "FALSE"/g' <VM>.vmx  

4. Confirm the changed which you have performed 
#cat <VM>.vmx | grep -i flash.enabled
 sched.scsi0:3.vFlash.enabled = "FALSE"
 sched.scsi0:5.vFlash.enabled = "FALSE"
 sched.scsi0:11.vFlash.enabled = "FALSE"
 sched.scsi0:12.vFlash.enabled = "FALSE"

5. after editing the VMX file, you need to reload the VM from command line or else from GUI
Now, try to POWER ON Virtual machine.

6. VM will be powered ON

Perform the same task for the VM which encounter the same problem.

Impact/Risks:
VM will not power ON