The News
Living Thin in a Fat World
We all seem to being living large in our personal livies and the same goes for the storage world. VMware has added Thin Provisioning as a supported feature with the launch of VSphere. It allows to size your virtual machine they way you want with out fighting will all the storage people. You could have thin provisioned your virtual machines hard drive in 3.5 with some work but now y ou can do it with ease.
When creating a vm or just adding another disk simply add the check box "Allocate and commit space on demand" and you're off to the races. The picture to the above points out that you can't use thin provisioning with Fault Tolerance enabled VM's. With the Record and Reply features working to protect the Fault Tolerant VM's the disks have to be Eager zeroed thick disks. This means all data is zeroed out at the time of creation so when a write operation occurs there is no waiting around.
Is it worth the headache?
It does add some additional management overhead but I think the benefits out ways the negatives. With thin provisioning you never have to use diskpart again on a windows box! Anything that can increase your up time and stop you from putting change orders in and making a lot of changes in the guest is a good thing.
I don't think you should rush off and convert every VM in your organization to a thin provisioned disk but start on some servers that do more processing than I\O and get a feel for the technology. You will want to setup alarms to make sure that you don't over commit to much. If you are someone that runs out of gas, this might not be right for you. You do have to monitor and watch your enviroment. VMware has two alarms, one for % Disk Usage on Disk and Datastore Disk Overallocation (%). Both will be helpful in managing your disk space.
% Disk Usage on Disk Alarm is a default right out of the box in vCenter 4.0, I had to add the Alarm for Datastore is Over commitment. I think the defaults for both alarms are ok but I think the key is to setup the alarm so team members are notified via email if things start to get carried away. You would hate to go on vacation if you're the only guy looking after things and walk into that mess.
Fragmentation, Is it a concern?
The VMware performance team is releasing a white-paper discussing performance concerns with thin provisioning. It looks like there is not much to be worried about at this point. If you feel that fragmentation is causing poor performance you have the ability to use Storage vMotion. When you use Storage vMotion it will but the blocks in order and you have the ability to convert your vmdk's to thin or think. This is great way to reclaim space on servers that you might have over provisioned. I think it would be best practice to have "Fixer LUN" in your environment that is running on some cheaper disk that you could always have handy to do this. Storage vMotion isn't tied into DRS yet but maybe down the road it will be and this process could be automated for us.
I am for one happy that thin provisioning is fully supported in Vsphere. The only thing I would like to see is the ability to have some sort of slider bar where you could have a thin\thick disk. For example, out of a 100 GB LUN, 50 GB would be thick and the rest would be thin. If 30 GB is being used by the volume some of the space is already zeroed out so performance is not affected. Then at a later time you could slide the bar over at night to zero out the more of the space. All in all, a great feature.