The following are configuration details for a three-node vSAN cluster:
• Each host has two disk groups and each disk group has 7×1.2TB 10K SAS drives.
• Each host has 16.8TB of raw capacity and the three-node cluster has 50.4TB of raw capacity.
• Deduplication and compression are not enabled.
Based on the following FTT Values in the storage policy, what is the total usable capacity?
A.
B. Cannot be calculated until vSAN datastore is online.
C.
D.
I disagree, I think the correct answer is B. None of the answers take into account slack space, which you can only confirm once the vSAN datastore is online.
The correct answer is D.
D should be correct.
https://livevirtually.net/2014/03/26/what-is-the-raw-to-usable-capacity-in-virtual-san-vsan/
With #FTT=1, VSAN can tolerate a single SSD failure, a single HDD failure, or a single host failure and maintain access to data. Valid settings for #FTT are 0, 1, 2, 3. If set to 3 then there will be 4 copies of the VM data thus RAW to usable would be 25%. In addition, there is a small formatting overhead (couple of MB) on each disk but is negligible in the grand scheme of things.
#FTT # Copies
(#FTT+1) RAW-to-usable Capacity %
0 1 100%
1 2 50%
2 3 33%
3 4 25%
Agree, D should be the correct answer.
Reference:
https://download3.vmware.com/vcat/vmw-vcloud-architecture-toolkit-spv1-webworks/index.html#page/Storage%20and%20Availability/Architecting%20VMware%20vSAN%206.2/Architecting%20Virtual%20SAN%206.2.2.022.html