Just because this thread comes up in Google, I would like to echo noctrex's answer in recommending WinBtrfs (GitHub), an experimental Windows Btrfs driver. Among its other features, it supports:
- Reading and writing of Btrfs filesystems
- Basic RAID: RAID0, RAID1, and RAID10
- Advanced RAID: RAID5 and RAID6
- Getting and setting of Access Control Lists (ACLs), using the xattr security.NTACL
- Hard links
- Sparse files
- zlib compression
- LZO compression
You can choose to mount it read-only after installation by modifying the registry entries in HKLM\SYSTEM\CurrentControlSet\Services\btrfs, and I've found it to be very stable (if a bit slow) even with six mounted Btrfs partitions and very frequent reads from one of them.
It does support writes to the disk, but as the software is still in development (and comes with the important disclaimer that "YOU USE IT AT YOUR OWN RISK. I take NO RESPONSIBILITY for any damage it may do to your filesystem. DO NOT USE THIS DRIVER UNLESS YOU HAVE FULL AND UP-TO-DATE BACKUPS OF ALL YOUR DATA"), it's probably inadvisable to not mount it read-only. (Unfortunately, by default it mounts with writes enabled, so you do have to go into the registry and change that. You should definitely have backups, in any case.)
Unfortunately, as the program is currently an unsigned driver, installation also requires enabling test signing by running "bcdedit -set TESTSIGNING ON" in the command prompt (followed by rebooting, right clicking on btrfs.inf from the WinBtrfs download, and clicking install). The GitHub page has full installation instructions.