Theory questions on Hyper-V

Question

Hello!

1) As you know there're two types of Live Migrations: in Windows Cluster or without clusters.

Q1: Am I getting it right that since in clusters both VM configuration and vhd are located on shared storage only the memory contents is to be migrated, while Live Migration without cluster should also include the VM's virtual hard drives (along with the configuration data, of cause), thus making the migration considerably longer than in a cluster?

2) https://www.altaro.com/hyper-v/virtual-networking-configuration-best-practices/

Cluster Shared Volumes: CSV traffic is not a unique role; it travels as part of standard cluster communications. When all is well, CSV traffic is fairly minimal, only passing CSV metadata information between the nodes. If a CSV goes into Redirected Access mode, then all traffic to and from that CSV will be handled by the owner node. If any other node needs to access that CSV, it will do so over a cluster network. The cluster will ensure that the normal cluster communications, such as heartbeat, are not sacrificed, but any struggles for bandwidths will cause virtual machines to perform poorly – and possibly crash. If your cluster does not use CSVs, then this traffic is not a concern.

Q2: Is there a way to prevent CSV from going into Restricted Mode (meaning if the connection to the node's storage is broken just failover to another node and DON'T use any cluster network adapter for CSV-rediraction traffic)?

Thank you in advance,
Michael

Answer 1

Hey,

A1: Yes, you are right. Shared nothing live migration will move both compute and storage resources, thus, it will take more time.

A2. There us always a reason for a CSV to go into Redirected mode. The following article covers different possible scenarios:
https://techcommunity.microsoft.com/t5/failover-clustering/understanding-the-state-of-your-cluster-shared-volumes/ba-p/371889

You can use StarWind VSAN as a shared storage backend for a Failover cluster, in this scenario shared storage will be always available from the cluster. Might help:
https://www.starwindsoftware.com/resource-library/starwind-virtual-san-for-hyper-v-2-node-hyperconverged-scenario-with-windows-server-2016/

Cheers,
Alex Bykovskyi
StarWind Software
Note: Posts are provided “AS IS” without warranty of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose

Answer 2

Alex, thank you for the reply!

"There us always a reason for a CSV to go into Redirected mode. The following article covers different possible scenarios:" - yes, I know, but I don't understand why there's no possibility to avoid redirection (at least block-mode redirection) to mimic non-CSV cluster behaviour: LUN is not available - failover to other node... :(

Regards,
Michael

Answer 3

Hi @Mikhail Firsov

Common requirements for any form of live migration Windows Cluster or without clusters are listed below.

-Two (or more) servers running Hyper-V that:
Support hardware virtualization.
Use processors from the same manufacturer. For example, all AMD or all Intel.
Belong to either the same Active Directory domain or to domains that trust each other.

-Virtual machines must be configured to use virtual hard disks or virtual Fibre Channel disks (no physical disks)

You can dig up more from here https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/hh831435(v=ws.11)

Hope this resolves your Query!!

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