In the hybrid vSAN 6.6 of 4 nodes, every node has 800 GB SSDs, and 4 HDDs of 1.8 TB each. To calculate usable disk space, I multiply 4 with 1.8 to get 7.2 TB for each node and then multiply that by 4 to get 28.8 raw disk space for entire vSAN. Out of this, 10% will be lost in overhead, giving me available disk space of about 25.9 TB. To have FTT=1, I need to take out 25% space which will be lost if one node goes down, so I am left with about 19.4 TB usable space.
However I am told by a sales person that I will really have only 7.7 TB - due to mirroring and threshold, whatever they may be.
Please help me ascertain usable disk space for this vSAN. Is mirroring essential? Thanks.