I had a query recently from a partner who was deploying VMware Horizon View 6.1 on top of an all-flash VSAN 6.0. They had done all the due diligence with configuring the AF-VSAN appropriately, marking certain flash devices as capacity devices, and so on. The configuration looked something like this:
The they went ahead and deployed Horizon View 6.1, which they had done many times before on hybrid configurations. They were able to successfully deploy full clone pools on the AF-VSAN, but hit a strange issue when deploying linked clone pools (floating/dedicated). The clone virtual machine operation would fail with an “Insufficient disk space on datastore” error, similar to the following:
This was very strange, since obviously there was plenty of space on the datastore. So what we knew is that this operation had previously worked fine on hybrid configurations, but would not work on all-flash configurations. And we also knew that other pools types other than the linked clone pool could be deployed on the all-flash configuration.
The next step was to examine the policies used with each of the pools. When deploying Horizon View on VSAN, a number of policies are automatically created. The different policies have different capabilities. The list of auto created policies for View is shown here:
When the Replica Disk policy was examined, it contained a 10% flash read cache reservation value by default. This was the crux of the issue. With AF-VSAN, the caching algorithm was changed, removing the read cache, which meant that there was no longer a requirement to use Flash Read Cache Reservation in the policies. However the auto created policy for Replica Disks in View 6.1 has a flash reach cache reservation setting of 10% by default. Once this was modified, and set to 0%, the link clone pools (which reply on a replica disk) could be successfully deployed:
So if you plan on using VMware Horizon View 6.1 on top of an All-Flash configuration, and you wish to use linked clone pools, you will have to modify the Flash read cache reservation setting highlighted above and change it from 10% to 0%. This is already highlighted in KB article 2110786. A complete fix for this issue will be available in a forthcoming patch to vSphere 6.0.