HPE Community read-only access December 15, 2018
This is a maintenance upgrade. You will be able to read articles and posts, but not post or reply.
Hours:
Dec 15, 4:00 am to 10:00 am UTC
Dec 14, 10:00 pm CST to Dec 15, 4:00 am CST
Dec 14, 8:00 pm PST to Dec 15, 2:00 am PST
Array Setup and Networking
cancel
Showing results for 
Search instead for 
Did you mean: 

How many VM's per datastore

 
SOLVED
Go to solution
nathanulph41
Occasional Visitor

How many VM's per datastore

Hi,

I was reading this post regarding how many vm's to store in a datastore How big are your VMFS datastores/how many VMs?

So the 10-15-20 rules seems fairly well tried and tested, so it leads me to wanting to understand what is considered high, medium & low I/O. It seems fairly fundamental to understand this when designing a datastore layout.

Thanks

Nathan

1 REPLY
aherbert23
Trusted Contributor
Solution

Re: How many VM's per datastore

That whole purpose of limiting the number of VMs per datastore is to reduce the induced latency from queueing. Each ESX host by default has a queue depth of 32 per VMFS datastore. If your storage averaged 5ms latency for all IOs then the maximum theoretical IOPS before inducing latency would be: (1 host) * (32 queue depth) * (1,000 ms / 5ms average latency) = 6,400 IOPS before inducing latency from queueing. So if we had 10 high IO VMs this would equate to about 640 IOPS per VM. Giving each VM the equivalent to a stand alone host with 4 - 15k disk RAID. Thusly having 20VMs per datastore would reduce this to a potential of 320 IOPS per VM. These numbers are per host so as you add hosts you can have more than 10-15-20 per VMFS datastore so long as they are evenly spread across the ESX hosts in the cluster.