Win11 renders existing ReFS volume inaccessible for Win10

Copper Contributor

run Windows 10 Pro for Workstations on my desktop. Existing disks/volumes include a simple storage space consisting of 2 SATA SSDs ("Raid0") with one volume spanning the whole pool, which was formatted with ReFS. 


For testing purposes I installed the current Windows 11 Preview (21H2 Build 22000.160) under Windows 10 from ISO (Windows11_InsiderPreview_Client_x64_de-de_22000.iso) as follows: prepared an external SATA SSD in an USB3-enclosure by installing the Win11 Preview (flavor: Windows 11 Pro for Workstations) via dism in a VHDX file and manually created a bootloader on the USB-SSD to boot from the virtual disk (VHDX) by selecting the USB device through UEFI as boot device.


The system booted fine from USB and I was guided through the normal initial / first boot setup procedure of windows 11 until I got to the normal desktop. All internal disks showed up normally in Windows 11 file explorer, including the storage space volume as well as various further NTFS formatted drives/volumes.


HOWEVER: when I booted my original windows 10 again, the ReFS partition showed up as "RAW" and Windows 10 always asked me to format the volume. Rebooted several times, no change, all files and folders remain "lost" for Windows 10. This only applied to the ReFS volume / storage space - all NTFS drives were normally accessible.


When booting up Windows 11 again everything also on the ReFS volume is still there and, for example, could be copied to different locations. So data is actually still there (hopefully, still have to run some tests).


It seems that the preview of Windows 11 Pro for Workstations "automatically modified" the Storage Space and/or ReFS volume in some way, which renders it incompatible with Windows 10 Pro for Workstations. There was no dialogue asking for permission nor could I find any information on this behavior.


I can only hope this is a bug - such behavior is in my view simply not acceptable for any software, in particular software wanting to be considered as "professional", and even more so for a filesystem that claims to be "secure" and "reliable"... 


Will now test with a NTFS-formatted volume on the pool - if that works "back-and-forth" between Win11 and Win10, it really is an ReFS issue. 


EDIT & UPDATE: just booted Win11, accessed the NTFS-Volume, booted Win10 again - no issue. So either it's related to ReFS or to the first time setup of Win11 (after preparing the system drive with dism). I did not install win11 again, just booted the exiting install. 

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