When building the image for your VDI environment you may reach a point where recompose times get longer and longer. One possible reason could be the size of your image. I have found that the breaking point for a desktop is about 250GB image. This doesn’t mean you have a 250GB disk and you are using 50GB.
If you have 250GB or more in your gold image you may reach a point where recomposes are hours and hours long. You will probably also notice some slow disk access in the VM. Your users may complain but when you look in ESX Top you don’t see long disk que times. Well you probably have an issue and you don’t know it.
For me the issue was View Storage Accelerator. In our testing View Storage Accelerator’s breaking point was about 250GB. As soon as we turned it off in some of our larger pools recompose times went back to reasonable times and performance improved. I have seen a few environments hit this issue so just something to be on the lookout for.
To fix this simply disable Storage Accelerator once you encounter the long recompose times to see if it fixes it.