How to install Windows to allow shrinking the Windows partition easier in the future

If you ever need to shrink your Windows partition for any reason without the use of third-party software, you may have noticed that even with very little data on a disk, you generally cannot shrink the volume nearly as much as you might have expected. For example, if you have a 512GB SSD and there is only about 60GB space used in your Windows partition, you still find that you cannot make the partition smaller than about 250GB (this is just an example, real numbers will be different). One reason for this is that when you format a partition, Windows creates various pieces of metradata on the volume and some of that gets stored roughly in the center of the volume.

Yesterday, this idea hit me: What if I initially make my Windows partition tiny, say like 10GB, and I format it. Now, Windows creates the disk structures, and because the drive is only 10 GB in size, it puts some of that data only about 5GB into the volume. Now, right after having created it, perfom an "extend" operation to grow that partition and volume. Note that when you do this, Microsoft does NOT relocate the metadata. It remains just a few GB into this partition. The result? Under most circumstances, you should be able to shrink that partition by a lot more.

I tested my idea today and it worked perfectly.

I realize that doing this may be a pain in the neck for some people because it means creating the partitions prior to installing Windows. But, if you are automating Windows installing it becomes ridiculously easy. I only had to add two entries to my unattended answer file to make this change.

Been doing that for years with win7 installations. Not as small as 10gb, I used to do 40-60gb . Haven't bothered with it more recently.

1. You cannot shrink a volume if there are page file or file blocks which are marked as unmovable, blocking the resize.

It might be you have a lot of RAM, and Windows defaults to ~1.5x page file and positions the page file's blocks roughly where you can't shrink past it. One test would be to disable the page file in the install image (by modding the offline image's registry hive), and seeing if you're allowed to resize the same volume down.

2. Unless you know how to customize an image and add some scripting, you can't have dynamically sized disk layouts. Either you have a "best guess" fixed layout, or use some form of partition extension in the unattended file.

This is where the old "recovery partition comes before the Windows partition" problem started. Back in the old days, WinRE was never too large in size and didn't wildly require more disk space over time. For simplicity, it was easier to assign a fixed Recovery right after the reserved partition, and extend the Windows volume to the disk's end.

But now, MS advises we place the Recovery after Windows, so the Windows volume can be shrunk to grow the Recovery. If we don't do this, then Windows is liable to create a second Recovery and abandon the original Recovery we created at install time (wasting disk space).

Ideally you have some script which does the disk math, and assigns a fixed size EFI and reserved partitions, and figures out how far back to place the recovery partition. Without some scripting, you can't do that do. If you have a small starting Windows volume, it doesn't solve the problem of knowing where to locate the Recovery. Unless you know exactly the disk size in advance, and it's always going to be unchanged in total disk size.

A fixed layout may work for you, but it's not universal for other folks.

garlin said:

Ideally you have some script which does the disk math, and assigns a fixed size EFI and reserved partitions, and figures out how far back to place the recovery partition.

Click to expand...

The easy way (no calculations needed, perfect layout every single time):

Assume you want the recovery tools partition to be 1GB.

Create the EFI and MSR partition. Create the Windows partition without specifying a size. It will occupy all remaining space on the drive. Shrink it by 1GB. Create another partition without specifying a size. It will be exactly 1GB in size. Use the usual commands to make that last partition a recovery partition.

Easy!

You said "using an unattended file". Still need to call an outside script or command.

It's three files that are evil that will stop windows from shrinking the volume . Page file, swap file and hibernation file.
What i did was disable paging/swap/hibernate then reboot... deleting the files... shrink the volume.. enable them again.. and reboot.
I shirked the system drive to only have 5GB free, so it was bootable... if i ever needed that windows install again.

Marie SWE said:

It's three files that are evil that will stop windows from shrinking the volume . Page file, swap file and hibernation file.
What i did was disable paging/swap/hibernate then reboot... deleting the files... shrink the volume.. enable them again.. and reboot.
I shirked the system drive to only have 5GB free, so it was bootable... if i ever needed that windows install again.

Click to expand...

Those can be disabled before the install, if you modify the offline image's registry. So the page or hibernation file is never created. After the system is installed then you could re-enable them in the registry and reboot.

garlin said:

You said "using an unattended file". Still need to call an outside script or command.

Click to expand...

I put commands in the autounattend, nothing more. It simply uses diskpart. Example:

<RunSynchronousCommand wcm:action="add">
<Order>4</Order>
<Path>cmd.exe /c echo select disk 0 &gt; X:\diskpartUEFI.txt</Path>
</RunSynchronousCommand>

All the commands are piped to a text file used as a diskpart script.

garlin said:

Those can be disabled before the install, if you modify the offline image's registry. So the page or hibernation file is never created. After the system is installed then you could re-enable them in the registry and reboot.

Click to expand...

I have never tested that.. But i understand what you mean
I mostly just modify to rip out unwanted things before install.. But i never had that in my thought before. Often when i do install windows, i plan on using it, so i make the system partition in the size larger then i might need the next years.. Then when i reach a point where i feel i have no use for it, but its good to keep just in case.. Then i make it as small as possible but still usable.. so my other system can use that space instead.

But i will keep it in mind, as a good note to have in my cheat-sheet

i always partition the disk before a clean install 250GB C:drive the rest as a Home partition for everything else.
it maybe worth while mentioning that Windows likes a partition size of about 128GB for C:drive
and thats for any future full system upgrades.

best of like Steve ..