Windows – Are there good reasons to partition disks on Windows

First pitfall/issue - there's no support for VHD files in most third party products. For example, if you get a virus and you need to boot from an antivirus CD, the antivirus software won't scan inside the VHD. You'll scan, clean up the hard drive, and then when you reboot into Windows you'll still have the virus.

Next - backup images are going to be more complicated. If you use something like Acronis TrueImage for backups, you have to make sure to back up the contents of the VHD, not the VHD itself. The VHD's timestamp will change every time you use it, and so to backup software, it'll look like a huge file that has to be recopied to the backup every single time the backup runs. In reality, only a few files have changed inside the VHD, and you only need to back those up.

Next - you said "when reinstalling you just need a copy of the VHD" - imagine that your next OS isn't compatible with the disk partition style you chose. You have to copy the VHD off to another drive (like a USB drive) and then copy it back. Why hassle with that when you could just partition and keep it separate and stable? If you have to copy it off the drive anyway, you can use any partition imaging software like TrueImage or its open source clones to copy the partition to an external disk.

1. On hard disks, throughput and seeking is often faster towards the beginning of the disk, because that data is stored closer to the outer area of the disk, which has more sectors per cylinder. Thus, creating the swap at the beginning of the disk might improve performance.

2. For a 2.6 Linux kernel, there is no performance difference between a swap partition and an unfragmented swap file. When a swap partition/file is enabled by swapon, the 2.6 kernel finds which disk blocks the swapfile is stored on, so that when it comes time to swap, it doesn't have to deal with the filesystem at all.

Thus, if the swapfile isn't fragmented, it's exactly as if there were a swap partition at its same location. Or put another way, you'd get identical performance if you used a swap partition raw, or formatted it with a filesystem and then created a swapfile that filled all space, since either way on that disk there is a contiguous region used for swapping, which the kernel uses directly.

So if one creates the swapfile when the filesystem is fresh (thus ensuring it's not fragmented and at the beginning of the volume), performance should be identical to having a swap partition just before the volume. Further, if one created the swapfile say in the middle of the volume, with files on either side, one might get better performance, since there's less seeking to swap.

On Linux, if the swapfile is created unfragmented, and never expanded, it cannot become fragmented, at least with normal filesystems like ext3/4. It will always use the same disk blocks, which are contiguous.

I conclude that about the only benefit of a dedicated swap partition is guaranteed unfragmentation when you need to expand it; if your swap will never be expanded, a file created on a fresh filesystem doesn't require an extra partition.