Thin provisioning?

[njd62495]

I'm still foggy on this whole thin provisioning thing. So let me work it out here and anyone PLEASE let me know if my thinking is correct. Sorry I have to ask the question we're still a few months away from getting to play with vSphere in our dev environment.

To keep things simple lets just say I'm using vSphere to do virtual thin provisioning (thick provisioning is done on the storage array).

So I carve out a 500 GB datastore for vm's whose disks will be thin provisioned. We'll say I have 5 vm's each with an 80 GB thin provisioned vmdk file and each vm is only utilizing 50GB of that allocation.

I understand that each VM cannot go above it's 80 GB allocation without extending the vmdk file. If the server is a Windows server (2003 or 2008), if I click on my computer will it show me a 50 GB drive that is 100% utilized? But if I go into the disk management snap in will it show an 80 GB partition with 50 GB formatted and in use (blue) and 30 GB as unallocated space (black)? Kinda like what you would see if you only partition 10 GB of a 100 GB physical disk.

If this is true my other question is, lets say SERVER1 is the only server to use up its thin provisioned 80 GB allocation and needs another 200 GB, if SERVER2-5 technically have 30 GB of available unallocated space and 100 GB is still available on the datastore, would I be able to shrink the unallocated space on 2-5 giving it back to the datastore and then allocate my addtional 200 GB to SERVER1?

If that's the case I need to start pushing alot hard to get vSphere implemented in our prod environment where we are out of SAN space allocation wise but we are only at about 25% utilization. I would love to be able to easily cut down some of the WE NEED a 100GB vmdk file only to find out 6 months later they have only used 3 GB.

[vmroyale]

Hello.

If the server is a Windows server (2003 or 2008), if I click on my computer will it show me a 50 GB drive that is 100% utilized?

No, it will show you an 80 GB disk that is 62.5% utilized.

But if I go into the disk management snap in will it show an 80 GB partition with 50 GB formatted and in use (blue) and 30 GB as unallocated space (black)? Kinda like what you would see if you only partition 10 GB of a 100 GB physical disk.

No, it will show a single 80 GB partition. The Guest OS doesn't know that it is using thin provisioned storage. It will report and behave just as if it had all of the space truly allocated to it.

If this is true my other question is, lets say SERVER1 is the only server to use up its thin provisioned 80 GB allocation and needs another 200 GB, if SERVER2-5 technically have 30 GB of available unallocated space and 100 GB is still available on the datastore, would I be able to shrink the unallocated space on 2-5 giving it back to the datastore and then allocate my addtional 200 GB to SERVER1?

You could give SERVER1 another 200 GB, so long as your total used space does not exceed the available space in the datastore. Some free space always is a good idea too!

If that's the case I need to start pushing alot hard to get vSphere implemented in our prod environment where we are out of SAN space allocation wise but we are only at about 25% utilization.

vi3 also supports thin disks, but a lot of routine operations tend to undo them. It can be done, but it is easier with vSphere. Possibly the biggest advantage with vSphere is the reporting for datastores, so that you can get warnings as your storage starts to fill up. These are missing in prior versions. Again, vSphere makes life easier.

I would love to be able to easily cut down some of the WE NEED a 100GB vmdk file only to find out 6 months later they have only used 3 GB.

Thin provisioning gets you the coverage for this. Keep in mind the consequences of overcommiting disk space, and set up alerts so that you can be proactive. Also, make sure not to overcommit to the point that you get into a hole that you may not be able to dig out of. If 3 users ask for 100GB and they all decide to use it up at the same time when you only have 100 GB total, it could be a very bad day.

Some other things to keep in mind are:

1. Running defrag utilities inside a Windows virtual machine will cause the associated thin disk(s) to grow to varying degrees.

2. When a thin provisioned disk grows, a SCSI reservation takes place.

3. If performance is the primary concern for a particular virtual machine, thin provisioned disks should not be used.

There is a ton of information in the forums about thin provisioning, and the What Is New in VMware vSphere 4: Storage whitepaper is also a good read.

Good Luck!

[DSTAVERT]

If I could just add that it isn't just 3.5 that will thicken disks when you least expect it (always expect it and plan for it) it happens in 4 as well.