It’s not just an urban legend. In this age of thin provisioning and growing snapshots, datastores really can (and do) run out of space! vSphere 5 luckily handles it a little better than the previous versions, which just automatically shut down you virtual machine. Now vSphere 5 will simply pause the machine. However, there are some new storage features with vSphere 5 that can help administrators manage their storage more efficiently…and maybe even optimize performance at the same time!
There are many resources available on the subject of SDRS (Storage DRS) on the VMware website or vExpert blogs, but I found the book VMware vSphere 5 Clustering Technical Deepdive by Duncan Epping and Frank Denneman to be very informative. SDRS is a lot like the current DRS, but it applies to storage. If a datastore starts running out of space or I/O resources, SDRS can transfer a virtual machine to a more appropriate datastore. In Chapter 20 of their book they state “Storage DRS (SDRS) bring this to a whole new level by providing smart virtual machine placement and load balancing mechanisms based on space and I/O capacity.” SDRS is a proactive strategy.
SDRS is accomplished by creating a datastore clusters. Sound familiar? This is a lot like using ESXi host clusters to implement DRS. Creating a datastore cluster is a matter of a few point and clicks of the mouse. You’ll need to plan how many datastore clusters you would like to create and which datastores will go in each cluster. Most likely you will analyze what kind of storage you have. It’s recommended that you keep like datastores together, as it will increase performance. For example, if you had a datastore using SSDs, you would keep those separate from slower storage. You might create a “gold” datastore cluster consisting of SSDs and a “silver” datastore cluster of RAID-5 SATA drives. You would want your virtual machines that demand more storage I/O resources to possibly use the gold datastore cluster…you get the idea.
There are a few caveats to watch out for. If you upgraded to vSphere 5 from a previous version, you more than likely have VMFS 3. There is an upgrade option from VMFS 3 to VMFS 5 available that doesn’t cause any interruptions to the virtual machines on that datastore. This may cause problems with storage migrations later on, though. Your best bet, before enabling SDRS, is to do a “rip and replace” of your current VMFS 3 datastores. This would mean storage migrating the virtual machines on the datastore to another datastore with available space. Then removing the now empty datastore. When that task has completed, you may add it back and it will give you the option of creating a VMFS 3 or VMFS 5 datastore. Pick the VMFS 5 option. Although it’s a little more time consuming, this method could save you a lot of troubleshooting in the future.
How to create a datastore cluster:
1. Open vCenter and go to the Home tab.
2. Click on the Datastores and Datastore Clusters option
3. Right click on your Datacenter
*Note: Datastore clusters cannot travers multiple datastores
4. Select the New Datastore Cluster option from the pull-down menu
5. A wizard will open. Provide a name for your datastore cluster and make sure there is a check mark next to Turn on Storage DRS.
6. Choose No Automation (Manual) or Fully Automated.
*I decided to use No Automation for now, at least in the testing phase. No Automation makes recommendations to move virtual disks to other datastores that either have more space available and/or better I/O resources. Fully Automated makes the changes automatically without getting administrator input.
7. You can accept the defaults for the next couple steps of the wizard.
8. When it’s time to select datastores, choose the datastores you’d like to put in this cluster.
Since we chose the No Automation method, we’ll need to check the recommendations SDRS has made manually. To do this go to Home>>Datastores and Datastore Clusters. Highlight the datastore cluster and then choose the Storage DRS tab. All of the recommendations will be listed and selected by default. You can click the Override Storage DRS Recommendations and select them individually if you so desire. Then click on Apply Recommendations and the appropriate tasks will execute.
This manual method, although safe, may go unnoticed by administrators. To combat this, you might decide to create an alert notification that gets triggered whenever there is a Storage DRS alarm. To set this up, highlight vCenter at the top of the tree on the left. Click on the alarms tab, right-click the Storage DRS Recommendations and choose Edit Settings. From this menu you can set it up to email you whenever this alarm is triggered.
There are many more details surrounding the implementation Storage DRS, but this brief overview is enough to set it up and start using it. With alarm notifications you get the best of both worlds. Using this strategy you won’t get caught off guard if SDRS tries to automatically storage vMotion a virtual machine using full automation, but you will be immediately notified of any recommended changes.