Friday, 2 June 2017

Azure Site Recovery (ASR) A few lessons learned....

A few useful things to keep in mind while utilising Azure Site Recovery from Hyper-V without VMM.


Azure Site Recovery replica traffic cannot be routed over a dedicated DR link

At the time of writing, you cannot route Hyper-V replica traffic over a dedicated network. By default, the management network is used for all ASR/Hyper-V replica traffic. Some client I have worked with maintain a 2nd Internet line which is usually dedicated for "DR" traffic. 

Hyper-V hosts loose connectivity to Azure when the agent gets out of date

An agent is required which is installed on the Hyper-V host servers in order to protect VM’s with ASR. The agent is constantly updated by Microsoft and I have found that the hosts lose connectivity if you are using an out of date agent. Generally, a simple reinstall/register resolves the issue.

Hyper-V VM disks cannot be converted to “protected disks” once the VM is protected

Once you have protected an on-premises VM using Azure Site Recovery, be sure to select all the required Virtual Hard Disk (VHD) files that belong to that VM. Once a VM is in the “protected” state (after the initial seed) you cannot protect additional disks that belong to that VM.

Add 25-50% extra bandwidth than the Azure Site Recovery Capacity Planner suggests

Microsoft has provided the following tool to help calculate the required amount of bandwidth to protect [x] amount of VM’s using Azure Site Recovery.


In my experience always add 25-30% to the suggested amount of bandwidth. Most of the recent Azure Site Recovery projects I have done recently are for small to medium sized businesses in the Caribbean so this may vary depending on what information you put into the capacity calculator.

Microsoft do not support Import/Export for Azure Site Recovery seeding

Microsoft does not offer the Import/Export services for Azure Site Recovery protected workloads, at the time of writing this post the only way to perform the initial “seed” of your protected VM’s is to do it over the WAN. Azure Site Recovery is based on Hyper-V Replica which was shipped in Windows Server 2012 and replica traffic is optimised to go over the WAN.

In the Caribbean Internet bandwidth is limited and very expensive, therefore customers are going to look at other solutions to protect their infrastructure over Azure Site Recovery. It would not be practical to replica a large number of VM’s to Azure using a typical Cayman Islands business grade DIA connection which might offer bandwidth in the region of 20-50 Mbp/s.

Microsoft needs to introduce the ability to ship an encrypted hard disk to their facility for offline data ingestion, otherwise up take in the Caribbean regions will be limited.

Extra Disk space is required on the source Hyper-V server to perform the ASR seed

ASR effectively takes a snapshot of the protected VM while it syncs it to Azure. Disk space is required on the source Hyper-V infrastructure in order for this to complete successfully.

Always move the page file to a dedicated disk, and ensure this disk is not protected with ASR

Self-explanatory.

Fixed size VHD’s work the bes

Although ASR fully supports Microsoft’s latest virtual hard disk files (VHDX), Azure natively only supports VHD’s at this time. VM’s which have VHDX disks are automatically converted to VHD files on the fly. In my experience, if the success rate is better if you use VHD files on the source VM’s, in addition to this I prefer to use fixed size disks when possible. I’ve seen some issues when protecting differencing disks. The errors are mostly related to the AVHDX which is created during the initial sync. 

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