SSD fails to attach to VirtuCache

If you get an error of the type:
“Failed: Assign SSD for Caching on host”
while trying to assign an SSD to VirtuCache, then its most likely because of any of the below reasons.

1. The SSD is being used as a VMware Datastore. If so, you will have to unmount and delete the Datastore before assigning it to VirtuCache.

2. The SSD is being used as a VMware boot device. You will have to delete the partition and move the VMware boot to some other local device or configure VMware to boot from SAN.

3. The SSD is being used with VMware VFRC. You will have to delete vFlash allocation for each VM that uses VFRC and then disable VFRC at the host level.

4. There is insufficient memory on the host to attach the SSD to VirtuCache. Typically if the SSD is 3TB or larger and there are many VMs running on the host, then this condition might be hit. Moving the host to maintenance mode and then assigning the SSD to VirtuCache will fix this issue. This link has more details on this error condition.

There could be other reasons as well, for instance, the SSD might be in use with some other software (another host side caching software or hyper-converged software like VSAN).

VirtuCache needs exclusive access to the raw (not formatted) SSD. Also once VirtuCache is assigned the SSD, it takes over the entire SSD and doesn’t share it with VMware or VMs. So if it’s used for any other purpose after the SSD is assigned to VirtuCache, VirtuCache will forcefully format the SSD and take control of it exclusively.