vSAN datastore question

[ScottSzcz]

Sorry, VMware new guy here. I'm currently setting up a vSAN environment. All my health checks are happy but there's something that's confusing me a little. I have 3 nodes with 800GB cache and 7TB capacity (all flash) but my datastore shows a total of 21TB. Am I missing a raid configuration within vsphere?

[paudieo]

the 800GB cache drives do not count against capacity of the datastore
only the capacity drives   count toward the raw capacity of datastore 
so each DG has a total raw capacity of 7TB and this aggregates to 21TB

more info here https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.vsan-planning.doc/GUID-581D2D5C-A88.... 

[ScottSzcz]

Thank you. The part I was confused about was I was expecting the datastore to be 7tb like a traditional raid would.

[paudieo]

yes its different in vSAN as you account for raid overheads when you build your VMDKs via storage policy 

e.g.when you set your policy to RAID-1 (Mirroring) and your virtual machine you must double the potenial overhead
so a 1 TB VMDK in fact will use 2TB vSAN capacity

[lukaszzasko]

Hi,

Total capacity on VSAN Datastore never include capacity of cache disks. If you have 3 x 7TB disks the total datastore space will be 21TB. This is RAW capacity without any raid.

You can create raid on virtual machine object level:

- for Raid 0 each 100GB space will consume 100GB on VSAN datastore

- for Raid 1 each 100GB space will consume 200GB on VSAN datastore