SRM Tutorial Part 2: Components & design

This part will give you an understanding of each of the components required in a SRM environment and also information you should consider for your own design.


SRM Tutorial Part 1: Lab setup
SRM Tutorial Part 2: Components & design
SRM Tutorial Part 3: SRM installation
SRM Tutorial Part 4: NetApp Ontap Simulator – Setup & configuration
SRM Tutorial Part 5: Configure NetApp SnapMirror
SRM Tutorial Part 6: SRA installation
SRM Tutorial Part 7: Configuration #1
SRM Tutorial Part 8: Configuration #2
SRM Tutorial Part 9: Advanced configuration & troubleshooting


I start again with a diagram, which shows all relevant logical components of the vSphere and SRM stack.

srm_diagram_detail

The vCenter Server of course remains the core of the VMware infrastructure, also when SRM comes into the game. It´s a requirement to have a vCenter instance on each site, which also means you will need an additional vCenter license.
You can connect both vCenter Server via the link mode feature like you may already have done it in your existing environment. If you are totally new to SRM I would suggest you to keep the vCenter instances independent on the beginning. I think this makes it more clear that you are really using to separate environments.

The SRM Server is shown on the diagram as a separate object, but it´s not a requirement to install SRM on a separate server. Still it is best practice to do this, which is also stated in the official SRM documentation. This is also one of the mostly asked questions, when it comes to SRM.
Especially for small environments one of the biggest arguments against a separate server are the additional licensing costs for another Windows instance. I think it´s absolutely sufficient to run vCenter and SRM on a single server, if you having just a small environment. I have seen a productive environment with around 60 protected VMs running without any problems. I wouldn´t say there is a fixed number of VMs where you definitely should run SRM on a separate server, but if your environment has around about 100 VMs or less you can consider to use just a single server.
If you have a Windows Server Datacenter license or if the additional license costs doesn´t matter to you, I would definitely go with a dedicated SRM server because there still some other benefits of running it separately. Once I have seen problems with the SRA (the adapter which communicates with the storage array), which required several reboots of the SRM server. In this example this means you have also a downtime of your vCenter server, if you are using a shared server for both services.

The same question often shows up when it comes to the database for SRM. Even if the diagram shows the vCenter DB and SRM DB apart from each other doesn´t mean that they can´t run on the same database instance. The common design includes a vCenter server, a SRM server and a DB server hosting both databases (vCenter and SRM). You need to keep in mind that the SRM database doesn´t contain so much data, so normally it is no problem to put it beside another database.

If you are using array replication (like we do in this tutorial) you will need a SRA (storage replication adapter). These adapters are provided by the respective storage vendor, but normally also available in the VMware SRM download section. The SRA gets installed on the SRM server and directly communicates with the connected storage systems.

Next in this construct we have the storage systems. If you haven´t done it already you should make sure in the first step if your storage system is supported for VMware SRM on the HCL. In combination with the SRA the array replication becomes “visible” to your virtual infrastructure, which is normally happens invisible on the array (which is physical still the case). I think the correct design of the storage systems if mostly much underestimated especially in huge environments.
That’s a topic which would be definitely worth a dedicated article, so on this point I´m just going to mention some considerations.
Often you don´t want to protect all your VMs, just the important ones (SRM 5 is licensed on a per VM basis). Due to the fact the array replication is done on per LUN or volume (or however each vendor´s specific name is) this can lead to frustrating situations, if you are not installing a complete new infrastructure from the ground up. You must see always the relationship of the VMs to the (replicated) datastore. In case of a disaster (or planed migration) SRM will switchover the complete datastore on the array level, which means you can´t have VMs with and without SRM protection on the same datastore.
Much more complicated it can become if you want to implement very specific and detailed DR plans. Let´s say you want to have the possibility to failover just a specific group of VM´s. Example you are hosting VMs for customer A and customer B. To implement dedicated and independent DR plans it´s necessary also to have a separation on the datastore layer of these VMs. Before implementing SRM often the focus for the storage design has been on values like performance and capacity. For most environments SRM brings now a totally new “view” into considerations, which can lead in the worst case to a totally new storage design. If this applies to you believe me you will appreciate the storage vMotion feature much more as before 🙂

Last but not least it´s worth mentioning how SRM is administrated. You will need to install a SRM plug-in for the vSphere Client to configure SRM. This you will see in detail in the following parts.



<< Part 1: Lab setup                   Part 3: SRM installation >>




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