Refer to the exhibit. A solution architect is setting up a highly resilient vSAN hybrid cluster. Why is the cache incorrectly sized in this configuration?
A.
Cache disk needs to meet vSAN Compatibility Guide
B.
Cache-to-capacity ratio needs to be sized lower
C.
Cache-to-capacity ratio needs to be sized higher
D.
Number of cache disks in disk group is insufficient.
I think Answer C is correct.
As a guideline, VMware recommends having at least a 10% flash cache to consumed capacity ratio in Hybrid vSAN configurations.
If you have 36TB capacity, you will need 3,6TB cache - But there you only have 1,2 TB cache.
The flash caching device must provide at least 10 percent of the
anticipated storage that virtual machines are expected to consume, not
including replicas such as mirrors.
In this case you have Only 1.2 TB cache because there are no required cache disks to reach 3 cache devices per node * 4 nodes to be compliance with the 10% cache required as per vSAN Design Guide
I vote C because it looks like they forgot to multiply capacity disks per host to get the cluster number. Cluster capacity is only 5 disks for capacity and is wrong.
B.
Cache to Capacity ratio needs to be lower. A "low ratio" means a larger-sized cache drive compared to capacity. I think it's a trick question, which is silly because this exam should be to ensure we know the content, not trick us with words.
Here is a reference to VMware calling it "high ratio" meaning you need more cache:
https://core.vmware.com/resource/vmware-vsan-design-guide#sec4-sub6
The correct answer is C.
Best practice: Ensure there is enough cache to meet the design requirements. The recommendation for cache is 10% of of the anticipated consumed storage capacity before the NumberOfFailuresToTolerate is considered.
If the RAW Capacity for each host is 36TB then the cache should be 3.6 TB for each host.
https://core.vmware.com/resource/vmware-vsan-design-guide#sec5-sub5
The correct answer is C.
Best practice: Ensure there is enough cache to meet the design requirements. The recommendation for cache is 10% of of the anticipated consumed storage capacity before the NumberOfFailuresToTolerate is considered.
https://core.vmware.com/resource/vmware-vsan-design-guide#sec5-sub5
I thing C is correct, cache is undersized on that diskgroups, Vsan disk groups only need a cache disk correctly sized, but take into account that on all flash the limit of usable cache is 600GB
Last row of first table states required cluster cache capacity is 3.6(equates to 9 disks) however with 12 cache drives of 400GB, it should be 4.8 so chache is incorrectly sized. Correct answer is D
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