vsan datastore capacity size calculation

[Ranjna Aggarwal]

In this screenshot i want to understand how vsan datastore size is calculated like here we have 3 nodes with 2tb capacity disks and vsan datastore size is 5.9tb. If i have 8tb disk each what vsan datastore size would be. Is there any formula for calculating the same?

[Ramesh Dhanaraj]

unlike other storage vendor capacity calculation, VSAN is a bit complex and  in order to calculate the capacity, many things are needs to be considered such as no.of VMs, vmdk size of each VMs, storage policy setting, number of FTT / VM or number of stripes per object and etc. However, there is official capacity calc available https://vsantco.vmware.com/vsan/SI/SIEV

sample capacity overhead are below

[Duncan Epping]

with 8TB disks it would be: 3 x 8TB - (some overhead) = total raw capacity

[Ranjna Aggarwal]

Thanks. What is this some overhead, what is this value? is there any formula i can refer as if i need to plan for sizing how can i go for overhead part?

[zdickinson]

Good morning, I'm sure there is some way to figure out the overhead; but in this case I don't think it's worth it.  We're talking a few hundred MBs.

In your case 8 TBs x 3 hosts = 24 TBs raw.  I'm guessing that's going to report as 23.9 TB usable.  If you place a 1 TB VM on it with FTT = 1 that will go down to 21.8 TB usable.  2 TB for the copies of the data and bit for the witness and meta data.

Thank you, Zach.

[Ranjna Aggarwal]

lets assume there is no vm and if i am enabling the vsan then what would be size of the datastore as depping said it is 3hosts x 8TB = 24TB - overead? i want to understand this overhead part.

[zdickinson]

From:  http://www.vmware.com/files/pdf/products/vsan/VSAN_Design_and_Sizing_Guide.pdf

Virtual SAN version Format Type On-disk version Overhead

5.5 VMFS-L v1 750MB per disk

6.0 VMFS-L v1 750MB per disk

6.0 VirstoFS v2 1% of physical disk capacity

Thank you, Zach.

[Ranjna Aggarwal]

In My test environment i have 6 disks of 6GB each across 3 esxi hosts and 2 per disk groups so total capacity is 36GB but datastore size is 34.45GB and i am using vsan 6.2 so this means it is not 1%.