An All-Flash vSAN cluster has 4 nodes with this disk group composition on each host:
✑ 1 × 800 GB SAS SSD
✑ 6 × 3.84 TB SATA SSD
An administrator observes that in an All-Flash cluster, the Write Buffer Free Percentage is consistently low. As a result, there is increased latency experienced by the workloads.
Which remediation steps will resolve this issue?
The consistent low Write Buffer Free Percentage in the All-Flash cluster is an indicator that the current cache device is being overwhelmed due to insufficient caching capacity. Adding a second disk group with a new cache device and distributing the capacity disks equally will significantly increase the overall caching capacity. This approach does not require replacing existing hardware, thereby avoiding the complexity and higher costs associated with changing cache devices in existing disk groups. It also allows for better scalability and utilization of cache resources, improving the efficiency and performance of the write buffer.
I think A.
is correct based on VMware recommended approach as D requires far more work, It is relatively easy to scale up both cache and capacity together with the introduction of new disk groups. It is also easy to add additional capacity by inserting new agnetic disks to a disk group in hybrid (orflash devices for all-flash). But it could be much more difficult to add additional cache capacity. This is especially true if there is a need to swap out the current cache device and replace it with a newer larger one. Of course, this approach is also much more expensive. It is far easier to overcommit on flash resources to begin with rather than trying to increase it once vSAN is in production. Design decision: Design with additional flash cache to allow easier scale up of the capacity layer. Alternatively scaling up cache and capacity at the same time through the addition of new disks groups is also an easier approach than trying to simply update the existing flash cache device in an existing disk group. https://core.vmware.com/resource/vmware-vsan-design-guide#sec6843-sub8
D is correct
A should be correct
Answer A. There is a 600GB Cap on Cache disks in vSAN 7.
Cache Must be 10% of capacity
Ignore not quite correct - see my other comment