John Savill FAQs on IT Pro

Storage Spaces Direct Across Locations; Mixing OS Types on Azure; Using Hyper-V to Protect Resources

John Savill's Frequently Asked Questions

Three times a week (Monday/Wednesday/Friday), John Savill tackles your most pressing IT questions.

Read through the FAQ archives, or send him your questions via email.

Q. I have heard some recommendations to not mix Windows and Linux VMs on the same subnet in Azure. Why?
Q. Can I stretch a Storage Spaces Direct cluster across locations?
Q. What is Hyper-V Host Resource Protection?

Q. I have heard some recommendations to not mix Windows and Linux VMs on the same subnet in Azure. Why?
Dept - Azure

A. This is not a limitation and mixing Windows and Linux VMs in the same subnet is fully supported and works. The only reason I have seen to separate Windows and Linux VMs into different subnets is to ease management of Network Security Groups.

Network Security Groups enable rules to be created which control the flow of traffic based on IP ranges and protocols. Rules are grouped into NSGs and then applied to a subnet. Typically Windows and Linux operating systems use different ports to communicate and so the reason to separate would be to have Windows targeted NSGs applied to Windows subnets and Linux targeted NSGs applied to Linux subnets however this is not required and an NSG could be created to support both types and applied to a single subnet.

Q. Can I stretch a Storage Spaces Direct cluster across locations?
Dept - Storage

A. Storage Spaces Direct (S2D) performs synchronous replication between the nodes in the cluster which means it is very sensitive to latency. For this reason it is not supported to stretch a S2D across locations. It also would not be very functional as there are 3 copies of any piece of data. If you split a S2D over two locations you would have 2 copies in one location and 1in the other. If there was some failure then you may end up with the live location having 1 copy of data meaning a single drive failure would mean data loss.

Instead the solution for DR is to have two separate clusters, one in each location with its own S2D instance. Then use a technology like Storage Replica or Hyper-V Replica to asynchronously send data between them.

Q. What is Hyper-V Host Resource Protection?
Dept - Hyper-V

A. New to Hyper-V in Windows Server 2016 is the ability to help protect the environment from a noisy, CPU hogging VM. When enabled if the system detects a machine using more than its fair share and impacting others its CPU will be throttled back. This is enabled on a per CPU basis and is disabled by default. For example:

Set-VMProcessor -EnableHostResourceProtection $True

 

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