Partitions: Windows 10 (Technical Preview) Requirements for WinRE


So I decided to have a look into the C:\Windows\Panther\setupact.log to see what Windows 10 needs as it relates to WinRE.  As a reminder I have a few other writeups on why the default partition sizes don’t work.  Head over to my Partitions page to read those

So here is what was in the setupact.log

Windows 10 Enterprise x86
	[setup.exe] winreMeetPartitionReq Required free space: 0x238DE882

Windows 10 Enterprise x64
	[setup.exe] winreMeetPartitionReq Required free space: 0x2633E3BC

Windows 10 Enterprise x64 UEFI
	[setup.exe] winreMeetPartitionReq Required free space: 0x2313E3BC

If I head over to the Hexadecimal to Decimal Converter I can convert them to Bytes.  Alternatively I can do this in calc (thanks Marcus Grant).

7-16-2015 10-05-04 AM

But anyway, you only care about the results right?

Windows 10 Enterprise x86
	[setup.exe] winreMeetPartitionReq Required free space: 0x238DE882
	596502658 Bytes = 568.87 MB Required
	WinRE = 199 MB
	Free = 370 MB
	
Windows 10 Enterprise x64
	[setup.exe] winreMeetPartitionReq Required free space: 0x2633E3BC
	640934844 Bytes = 611.24 MB Required
	WinRE = 241 MB
	Free = 370 MB

Windows 10 Enterprise x64 UEFI
	[setup.exe] winreMeetPartitionReq Required free space: 0x2313E3BC
	588506044 Bytes = 561.24 MB Required
	WinRE = 241 MB
	Free = 320 MB

So it appears that for BIOS Systems with an Active partition, the space required is calculated:
Size Required = WinRE Size + 320MB for VSS + 50MB for System Files

For a UEFI System it is calculated:
Size Required = WinRE Size + 320MB for VSS

UEFI is different since there should be no System files as they reside on a System Partition, so it doesn’t need to account for them.

So this means that on BIOS Systems, you can customize WinRE up to 50MB – System Files. Sounds great right? That is until you realize that 44.62 MB are consumed by System Files and NTFS overhead. So you have about 5MB of free space.
UEFI is a quite a bit more unforgiving. While the math seems sound, it does not account for NTFS overhead, boot.sdi, and ReAgent.xml. In my check, I have 267.79 MB used in my WinRE Partition. Since the required space according to Microsoft’s logic gave me 561.24 MB required, that means that I have 293.45 MB free in actuality, which violates the 320MB VSS Requirement.

Not good.  So does this really matter if you are not deploying Windows 10 now?  Absolutely, if you plan on doing any Windows 10 upgrades in the future, you should account for this now.

7-16-2015 9-56-47 AM 7-16-2015 9-57-02 AM 7-16-2015 9-57-05 AM

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