How can calculate the number of components for bandwidth in 2node

[baber]

According to vSAN 2 node cluster guide on page 25 for calculate bandwidth used follow formula:

1138 B * NumComp / 5 Seconds

for a workload such as follow :

 3objects { vm name space , vmdk (under255G) , and vmSwap}

FTT=1

Stripe = 2

2 Snapshot per VM

and we have 25 vms according to that doc we have 250 components

How did it calculate components ?

According to attach pic I have created a VM with above info and this vm has 16 components , thus 16*25 = 400

According to that doc it calculates 10 components for each VM . How it calculate?

[jburen]

AFAIK the FTT=1 doubles the three objects. So a VM with three objects would give you 6 components. But when you set the number of stripes to two, the number of components for the disk objects double once more.

FTT=1
VM object: 2 components
Swap object: 2 components

FTT=1 and Stripes=2
vmdk object: 4 components
snapshot1 vmdk: 4 components
snapshot2 vmdk: 4 components

So in total, you would have 16 components. Imho I think the documentation is still calculating with Stripe Width 1.

[depping]

Just reading it again, hmmm. pretty poorly documented. 

There are a couple of things to remember: Each object will get a witness object on the witness host, so for a VM with 1 disk:

VM name space --> witness
VM swap --> witness
VMDK --> witness

So for this VM configuration, it would be 3 witness objects stored on the witness. Now with the snaps and the stripe width, this would be 5*2, is 10, which means for 25 VMs this becomes 250. 

But this documented could even be outdated, I will ask the team to revise it.

[baber]

1- Is that your means we have to consider number of witness instead of number of components ?

2- If you see in the pic on first post I have create a vm with FTT=1 and stripe=2 and it has also 2 snapshot. But there are just  5 witness How did you find 10 witness in 2node for above scenario ?

[depping]

1) a witness is a component on the witness host, this is what you take in to consideration according to the documentation

2) they get to 10 based on the stripe it seems, I have not tested it, so I don't know at this point

[baber]

Thanks. But I think This part of document (Bandwidth calculation for vsan_2node) is not correct .

[jburen]

Based on the image you uploaded each object gets a witness component so with 5 objects (VM, swap, vmdk, snapshot1 and snapshot2) that would be 5 witness components.

[depping]

Correct, the documentation seems inaccurate, I just tested it in a lab, I will ask them to fix it. With, or without stripe, you still have 1 witness per object.