Storage DRS (SDRS) is another new feature of vSphere 5.0, and is possibly one of the most exciting.

It allows for intelligent initial placement and on-going space & load balancing of Virtual Machines across datastores in the same datastore cluster. A datastore cluster is simply a folder of datastores. Here is a view of one such datastore cluster, which contains 3 NFS datastores:


When Storage DRS is enabled on a datastore cluster, the datastore cluster becomes a load-balancing domain. You can place both VMFS-3 & VMFS-5 datastores in the datastore cluster if you wish, but the best practice recommendation is to place datastores which have the same capabilities into the same datastore cluster. You cannot mix NFS & VMFS datastores in the same datastore cluster.

When a datastore cluster is created, SDRS is automatically enabled, as shown here:

We will look at the load-balancing featues in a future posting, but in this post I want to talk about the initial placement, which is really a great feature. When you create or migrate a VM, you can choose the VM to be placed in a datastore cluster. SDRS will now pick the most appropriate datastore for this VM, based on available space and I/O latency:


In automatic mode, SDRS will chose a datastore for you. The other nice feature is that even if you have automatic mode selected for SDRS, when it comes to deploying or migrating a VM, you can still choose to do the initial placement manually if you wish.

To do this, at the Ready to Complete screen, select the 'Show All Storage Recommendations':

You can then choose which datastore to deploy your VM onto, as per the recommendations shown below:


One thing you may notice is that even when the cluster is in manual mode, you are not given any datastore to choose during deployment unless you select ‘Show all storage recommendations’ in the Ready to Complete window. This might give the impression that initial placement is indeed automated even when the cluster is manual. What is actually happening is that SDRS calls "Apply Recommendations" on your behalf and the top manual placement recommendation that SDRS provided is chosen for you.

My best practice recommendation around SDRS is pretty much along the same lines we gave customers when we initially released DRS back in the day – run everything in manual mode to begin with, and make sure that the recommendations that are being made to you by SDRS for initial placement of VMs make sense – check the space usage & latency of the datastores in the datastore cluster, and verify SDRS is selecting the best one. Once you see that the recommendations are indeed making sense, you can start to think about letting SDRS make these decisions automatically.

In future postings, I will discuss how Storage DRS does load balancing based on space usage and I/O metrics.