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I have two Windows 10 installations on a single GPT drive.

The current partition layout is: EFI WinRE MSR ...OS1... ...OS2...

Currently, OS1 is configured to use WinRE partition, as suggested here. OS2 does not have any WinRE yet.

Is it possible to:

  1. re-use existing (large enough) WinRE partition for both OS1 and OS2, or each installation requires separate WinRE?
  2. does answer (1) change if I will have to turn BitLocker on for OS2 per employer BYOD requirements?

Also:

  1. do "large" (i.e., feature) updates to both installations affect WinRE?

  2. is WinRE partition required to enable BitLocker, or this is wrong?

UPD:

My key idea (I'm asking about how to implement it) is to re-use 'auxiliary' partitions, if that's possible. I would like to be able to enable BitLocker on OS2 without having to re-partition the drive (even autoshrinking OS2 partition), so that OS2 should re-use existing EFI/WinRE partitions.

So:

  1. Is it possible to re-use existing (large enough) WinRE/EFI partitions for both OS1 and OS2, with at least one OS having BitLocker turned on?

  2. How should I configure OS2 to re-use one of these unencrypted partitions as a 'bitlocker-required unencrypted partition'?

  3. Does re-using partitions affects somehow stability (update of WinRE by feature updates) or security?

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  • You are aware that strictly speaking that the WinRE isn’t actually required. I see no reason you wouldn’t be able to use the same partition. Why are you against using two partitions? The single partition would have to be the appropriate size, so your not gaining any additional substantial storage space, by having a single partition
    – Ramhound
    Commented Oct 6, 2020 at 10:50
  • @Ramhound in many cases enabling BitLocker requires WinRE partition. Thus I'm interested in re-using the existing one because if I could use the very same WinRE for both OS, why should I lose ~900Mb of storage space for the second duplicate one?
    – simon
    Commented Oct 6, 2020 at 11:08
  • Are you using BitLocker now or planning on it?
    – harrymc
    Commented Oct 15, 2020 at 17:00
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    @simon - WinRE can be changed by feature updates see Updating the on-disk Windows Recovery Environment. As described a new partition is created if the existing is too small or otherwise incompatible. Bitlocker requires an unencrypted system partition - this is WinRE partition in BIOS systems or the EFI partition for you.
    – lx07
    Commented Oct 17, 2020 at 7:37
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    I can't post an answer as I don't know whether you can share WinRE. It might not be possible as according to here the GUID in bcdedit must match the GUID in ReAgent.xml in the WinRE partition. You could try checking reasons that the partition is not suitable by looking at reagentc log file. For example try running reagentc /enable /logpath c:\WinRE.log on both.
    – lx07
    Commented Oct 17, 2020 at 10:06

1 Answer 1

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I believe that it's possible to share one WinRE partition between multiple installations of Windows.

To set the WinRE partition in Windows, use the command reagentc in an elevated Command Prompt. For example:

Reagentc /setreimage /path X:\Recovery\WindowsRE

This requires assigning the WinRE partition a drive-letter in Disk Management, which can be removed afterward. The above path will be translated to an independent format, such as \\?\GLOBALROOT\device\harddisk1\partition4\Recovery\WindowsRE, so that the drive-letter is not required.

The specified folder should contain the file Winre.wim, which contains the WinRE image itself.

(I have never done it myself, but I think that this will work for you.)

Useful articles:

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4
  • I've done it before for OS1, so this works. The question is whether this won't "destroy" OS2, will have to give it a try
    – simon
    Commented Oct 15, 2020 at 19:45
  • I wouldn't think so. WinRE should be independent from any Windows installation since it's always re-invoked from the standard Winre.wim in vanilla condition.
    – harrymc
    Commented Oct 15, 2020 at 19:58
  • Do you also know, if "large" (i.e., feature) updates to both installations affect WinRE somehow?
    – simon
    Commented Oct 16, 2020 at 20:07
  • I don't know for sure, but it would surprise me if updating the system partition touched upon other partitions.
    – harrymc
    Commented Oct 17, 2020 at 6:00

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