Windows swap file: why do I have a 3GB swap file when I have 8GB RAM

VMware ESX admins have to pay attention to host swap file sizes because you can overcommit on memory. With Hyper-V, you can't overcommit on memory - for example, you can't take a host with 16gb of ram and start up 8 guests with 4gb of ram each. There's pros and cons to that approach. In a nutshell, though, you're right in saying it shouldn't need a host file - as long as you don't run anything on the host other than Hyper-V guests. If you remote desktop in and run things, or if you run third party backup or antivirus software on the host, you should set up a page file just to be safe. I've seen instances where people RDP into the host and run a backup software console written in Java, for example, and it needs gigs of memory in order to start & run a restore operation.

Pagefile fragmentation will only be a significant factor in extreme cases. Fragmentation is a factor when large files are read serially, but this almost never happens with the pagefile. Pagefile access is in small blocks of no more than 64K, and this will be usually mixed with access to other files. It matters little if the pagefile is fragmented or not, the disk heads will be moving around in any case.

None of this really matters unless pagefile performance is a limiting factor. And it usually isn't. Most paging doesn't use the pagefile at all. By design the pagefile is used to store data that is not accessed frequently. In most cases the pagefile isn't accessed often enough for it's performance to matter.

In most cases this is just much adu about nothing. The misquided attempts to solve the problem can, and often do, cause serious problems.