Stuck with VMware Error “Cannot create Flash Read Cache: Operation failed”? We can help you.

Often VMware users report to us that they get this error while trying to power on the VM.

Here at Bobcares, we handle requests from our customers to fix similar errors as a part of our Server Management Services. Today we will see how our Support Engineers fix this for our customers.

How to fix VMware Error “Cannot create Flash Read Cache: Operation failed”

Before going into the steps for fixing the error we will see what causes this error.
A typical error looks like the one given below:

Unable to power ON Virtual machine with Error: Failed to power on the virtual machine. Cannot create Flash Read Cache: Operation failed. (66927)

Cause

The SSD drive used as vFlash Read Cache (vFRC) was removed from the ESXi host in which a VM has been registered and configured to use vFRC, in the absence of an SSD card a power-on operation of VM will fail. As a result of this VM will not get Powered On.

Steps to fix this error

Following are the steps that or Support engineers follow to fix this error:

1. To power-on, the affected VM first we need to change the value from TRUE to FALSE for vFlash entry.

2. We must take the backup of the vmx file before editing the vmx file.

This can be done with the following command:

# cp <VM>vmx <VM>.vmx.backup

3. Now, using the vi editor we will change the disk value:

# vi <VM>.vmx
sched.scsi0:0.vFlash.enabled = "TRUE" and change to  "FALSE"

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 we must download the vmx file. And then change the value for .vFlash.enabled from TRUE to FALSE.

Following are the steps to implement it:

a. We can ist out all the disk which has vFRC enabled using the following command:

#  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"

b. After that we will take a backup of the VMX file. We can use the following command for this:

# cp <VM>vmx <VM>.vmx.backup

c. Now we can use the following command to change the value from TRUE to FALSE:

# sed -i 's/vFlash.enabled = "TRUE"/vFlash.enabled = "FALSE"/g' <VM>.vmx  

4. We can confirm the changes made using the following command:

#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, we need to reload the VM from the command or GUI line.

via Command line

We can use the following commands:

vim-cmd vmsvc/getallvms | grep -i <vmname>
vim-cmd vmsvc/reload <VMDI>

via GUI

We need to select the VM in the inventory and unregister and register the VM back from the datastore. Then we can try to POWER ON Virtual machine.

6. We can see that the VM gets powered ON

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Conclusion

In short, we saw how our Support Techs fix VMware Error “Cannot create Flash Read Cache: Operation failed” for our customers.