Exam 5V0-22.23 topic 1 question 4 discussion

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From the online vSAN course: Nested Fault Domains To improve the resiliency of a Two-Node vSAN cluster, vSAN OSA and vSAN ESA support nested fault domains. In a nested fault domain: • Each disk group (vSAN OSA)/disk (vSAN ESA) is turned into a sub-fault domain • vSAN OSA - components are placed on disk groups and mirrored/striped across disk groups in the same host • vSAN ESA - components are placed on individual disks and mirrored/striped across disks in the same host • Protects against disk group/disk failure • OSA Supports: RAID-1/FTT 1 and FTT 2 and RAID-5 • ESA Supports: RAID-1/FTT 1, 2, and 3 and RAID-5/6

https://www.vmware.com/docs/vmware-vsan-design-guide#sec6870-sub1 page 52

I feel that the question is transcribed poorly. For Raid 5 we need 4disk groups. But if we use ESA, we could make it work with raid 5 (2+1) . It is impossible to have something different than Raid 1/FTT1 when the question is asking for protection against a disk group failure and there are only 3 DG per host

B, E vSAN Storage Policies Number of Failures To Tolerate (FTT) - Pre-vSAN 6.6 Primary Number of Failures To Tolerate (PFTT) - vSAN 6.6 and forward The FTT/PFTT policy setting, has a maximum of 1 for objects. In Pre-vSAN 6.6 2 Node Clusters FTT may not be greater than 1. In vSAN 6.6 or higher 2 Node Clusters, PFTT may not be greater than 1. This is because 2 Node Clusters are comprised of 3 Fault Domains. Failure Tolerance Method (FTM) Failure Tolerance Method rules provide object protection with RAID-1 (Mirroring). Mirroring is the only FTM rule that can be satisfied, due to the 3 fault domains present. This means that data is Mirrored across both sites. https://core.vmware.com/resource/vsan-2-node-cluster-guide#section1

The first easy choice is answer E (RAID-1/FTT 1). The other FTT level (2 and 3), are impossible, as we have only 2 hosts in the cluster. RAID-5/FTT 2 is also totally impossible, whatever is the architecture of the vSAN cluster. The other answer will D (RAID-5/FTT 1) : not achievable by the administrator because he has only 3 disk groups, but technically feasable if the hosts have at least 4 disk groups each --> the question is not to know about what the administrator can do, but which storage policies can protect agains a disk or disk group failure.

There is only 3 disk group so raid5 on nested fault domain is not possible. But we can do a raid1 nested fault domain on the 3 disk group, so i think the answer is B and E. RAID5 on nested FD will be possible if 4 disk group per node. "If the hosts had four disk groups, RAID-5 erasure coding could be used for the secondary level of resilience, but one would have to run through an analysis to see if the cost of an extra disk group would be offset by the capacity savings noted above. RAID-6 is not possible in this topology." https://core.vmware.com/blog/sizing-considerations-2-node-vsan-clusters-running-vsan-7-u3

2 nodes only can have FTT = 1 RAID is for disk FTT is for nodes

D E. RAID-1 and RAID-5 are only options for a 2-node cluster. https://core.vmware.com/resource/vmware-vsan-design-guide#sec6870-sub1

A. RAID-5/FTT 2: This policy provides RAID-5 erasure coding with a failure-to-tolerate setting of 2, which can protect against the failure of one disk or one disk group. D. RAID-5/FTT 1: This policy provides RAID-5 erasure coding with a failure-to-tolerate setting of 1, which can protect against the failure of one disk or one disk group.

Don't see how one can have more than FTT=1 in a 2-node configuration

D and E are correct https://core.vmware.com/resource/nested-fault-domains-vsan#section1

D and E- supports Raid-1/fft1 AND Raid-5/FTT1 only Two-node Vsan cluster

2 nodes only can have FTT = 1 RAID is for disk FTT is for nodes