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Shōgun8
Asked: 2020-04-03 12:51:10 +0800 CST

How could the vSAN datastore capacity be equal to the raw capacity of the physical disks in an all-flash cluster?

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I have configured a new 3-node all-flash vSAN cluster as the default RAID 1 (only option). Each node has one cache drive and four capacity drives; the total capacity drive space of each node is 3280GB.

I have configured the vSAN datastore to use the 'vSAN Default Storage Policy', which it says will give me a FTT=1 ( a Failure To Tolerate ration of 1).

However, it tells me that I have a total usable capacity of 8.94TB; how can this be? Isn't that wrong?

vmware-vsan

1 Answers

  1. Best Answer

    So, I figured this out. Even though the vSAN is a RAID 1, it will report the raw disk capacity as the available storage capacity. However, when a VM is deployed, it will take up twice as much space as it normally would.

    In other words the mirroring occurs at a per VM level. From here:

    FTT FTM        Overhead   VM size       Capacity required  
1   Raid-1      2x        100GB         200GB  
1   Raid-5/6    1.33x     100GB         133GB  
2   Raid-1      3x        100GB         300GB  
2   Raid-5/6    1.5x      100GB         150GB
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