After installing VSC 4.0 and scanning my LUNs with the “Optimization and Migration Scan Manager” I wondered why all my VMFS 5.54 LUNs appeared as “not optimized”.
So I did some research in the NetApp documentations and communities to find out what this optimization/alignment tool is exactly doing to create an “optimized LUN”.
Unfortunately there was no deep dive documentation from NetApp (or I did not find it) about this – so if you see any mistake in my explanation please leave a comment. But you can leave a comment, too if you agree…
Part 1 – Create a VMFS 5.54 LUN with vCenter + a pre-aligned guest:
When you create a LUN with your vCenter 5.x wizzard and put a Windows 2008 (or newer) guest on it, everything is fine. Your guest will be pre-aligned.
You can check this with your NetApp “Optimization and Migration Scan Manager” – you will find these VMs in the “Aligned Tab”:
But if you check the LUN where these aligned VMs are running with the Scan Manger you will see that it is displayed as “not optimized”:
This happens because in the mind of the scan manager an optimized datastore only exists if the datastore is functionally aligned with the same offset as the the unaligned virtual machines running on it.
This means if you have 2008 (and newer) VMs on a standard created VMFS LUN – you have no problem. The Datastore and the guests are aligned even if the wizzard says “not optimized”. Because it is only not optimized for “unaligned VMs”!
Part 2 – Create a VMFS 5.54 LUN with vCenter + a misaligned guest:
When you create a LUN with your vCenter 5.x wizzard and put eg. a Windows 2003 VM on it you will see that it is not pre-aligned:
Part 3 – migrate the unaligned guest to an optimized datastore:
To align the VM select the “migrate” task in your VSC 4.0. This will open the following wizzard:
In the next step you can select between “use an existing datastore” and “create a new datastore”.
You can only use an existing datastore if you already have a LUN which is aligned with an offset corresponding with the one of the unaligned virtual machine. Most (or all?) 2003 VMs have an offset 7 for example.
If you select “create a new datastore” VSC will create a datastore which is intentionally offset in the same way as the unaligned VMs!
So the magic is:
Maybe this simplified graph will help you to understand:
The only difference is, that the optimized datastore is intentionally offset the same way like the unaligned VM.
So if you would put an aligned VM from a “standard datastore” on the optimized datastore, it will become unaligned!