OpenZFS ports
C Shell Roff C++ Python Objective-C Other
Clone or download

To setup a development environment for compiling ZFS.

Download free development Windows 10 image from Microsoft.

and create two VMs.

  • Host (running Visual Studio and Kernel Debugger)
  • Target (runs the compiled kernel module)

The VM images comes with Visual Studio 2017, which we use to compile the driver.

It is recommended that the VMs are placed on static IP, as they can change IP with all the crashes, and you have to configure the remote kernel development again.

Go download the Windows Driver Kit 10

and install on both VMs. You will need both the SDK and WDK: Download the SDK with the Visual Studio 2017 community edition first and install it. It will update the already installed Visual Studio. Then install the WDK. At the end of the installer, allow it to install the Visual Studio extension.

On Target VM, complete the guide specified here, under section "Prepare the target computer for provisioning".

Which mostly entails running:

C:\Program Files (x86)\Windows Kits\10\Remote\x64\WDK Test Target Setup x64-x64_en-us.msi

  • reboot Target VM

On the Host VM, continue the guide to configure Visual Studio 2017.

  • Load Visual Studio 2017, there is no need to load the project yet.
  • Menu > Driver > Test > Configure Devices
  • Click "Add New Device"
  • In "Display name:" enter "Target"
  • In "Device type:" leave as "Computer"
  • In "Network host name:" enter IP of Target VM, for me ""
  • Provisioning options: o Provision device and choose debugger settings.
  • Click "Next >"

It now confirms that it talked to the Target, and note here that "Host IP" it that of the Host VM, for me, "", and not to be confused by the Target IP entered on previous screen.

  • Click "Next >"

Watch and wait as remote items are installed on the Target VM. It will most likely reboot the Target VM as well.

I've had dialog boxes pop up and I agree to installation, but I am not sure they are supposed to. They probably shouldn't, it would seem it failed to put WDKRemoteUser in Administators group. If that happens, use "lusrmgr.msc" to correct it.

The task "Creating system restore point" will most likely fail and that is acceptable, however, if other tasks fail, you may need to retry until they work.

At the end of the run, the output window offers a link to the full log, which is worth reading if you encounter issues.

When things fail, I start a CMD prompt as Administrator, and paste in the commands that fail, from the log file. It would be nice if this process just worked though.

If your version of .NET newer, just move along.

The Target VM should reboot, and login as "WDKRemoteUser".

It is recommended you get GIT bash for Windows and install:

Host and Target VMs are now configured.

First time you load the project it might default to

Debug : ARM

you probably want to change ARM ==> X64.

  • Load ZFSin solution

  • Menu > Debug > ZFSin Properties

  • Configuration Properties > Debugging "Debugging tools for Windows - Kernel Debugger" Remote Computer Name: Target

  • Configuration Properties > Driver Install > Deployment Target Device Name: Target [Tick] Remove previous driver versions O Hardware ID Driver Update Root\ZFSin

You can run DbgView on the Target VM to see the kernel prints on that VM.

Run the compiled Target

  • Compile solution
  • Menu > Debug > Start Debugging (F5)

wait a while, for VS2017 to deploy the .sys file on Target and start it.

Target VM optionals.

If you find it frustrating to do development work when Windows Defender or Windows Updates run, you can disable those in gpedit.msc

  • Computer Configuration > Administrative Templates > Windows Components > Windows Defender Windows Updates


Compile SPL sources

  • Godzillion warnings yet to be addressed

Port SPL sources, atomics, mutex, kmem, condvars

  • C11 _Atomics in kmem not yet handled

Compile ZFS sources, stubbing out code as needed

Include kernel zlib library

Load and Unload SPL and ZFS code

Port kernel zfs_ioctl.c to accept ioctls from userland

Compile userland libspl, libzpool, libzfs, ...

Include pthread wrapper library

  • Replaced with thin pthread.h file

Include userland zlib library

Compile cmd/zpool

Port functions in libzpool, libzfs. Iterate disks, ioctl

Test ioctl from zpool to talk to kernel

Port kernel vdev_disk.c / vdev_file.c to issue IO

Port over cmd/zfs

Add ioctl calls to MOUNT and create Volume to attach

Add ioctl calls to UNMOUNT and detach and delete Volume

Port kernel zfs_vnops.c / zfs_vnops_windows.c

  • Many special cases missing, flags to create/read/etc

Correct file information (dates, size, etc)

Basic DOS usage

Simple Notepad text edit, executables also work.

Basic drag'n'drop in Explorer

zfs send / recv, file and pipe.

ZVOL support

git clone ZFS repo on ZFS mounted fs

Compile ZFS on top of ZFS

Scrooge McDuck style swim in cash

Design issues that need addressing.

  • Windows do not handle EFI labels, for now they are parsed with libefi, and we send offset and size with the filename, that both libzfs and kernel will parse out and use. This works for a proof of concept.

Possibly a more proper solution would be to write a thin virtual hard disk driver, which reads the EFI label and present just the partitions.

  • vdev_disk.c spawns a thread to get around that IoCompletionRoutine is called in a different context, to sleep until signalled. Is there a better way to do async in Windows?

  • ThreadId should be checked, using PsGetCurrentThreadId() but it makes zio_taskq_member(taskq_member()) crash. Investigate.

  • Functions in posix.c need sustenance.

  • The Volume created for MOUNT has something wrong with it, we are unable to query it for mountpoint, currently has to string compare a list of all mounts. Possibly also related is that we can not call any of the functions to set mountpoint to change it. This needs to be researched.

  • Find a way to get system RAM in SPL, so we can size up the kmem as expected. Currently looks up the information in the Registry. kmem should also use Windows signals "\KernelObjects\LowMemoryCondition" to sense pressure.

Thinking on mount structure. Second design:

Add dataset property WinDriveLetter, which is ignored on Unix system. So for a simple drive letter dataset:

zfs set windriveletter=Z: pool

The default creating of a new pool, AND, importing a UNIX pool, would set the root dataset to


So it is assigned first-available drive letter. All lower datasets will be mounted inside the drive letter. If pool's WinDriveLetter is not set, it will mount "/pool" as "C:/pool".

Installing a binary release

Latest binary files are available on GitHub:

Download your preferred package.

Enable unsigned drivers:

  • bcdedit.exe -set testsigning on

Then reboot. After restart it should have Test Mode bottom right corner of the screen.

  • Right click on ZFSin.INF file
  • Select "Install"
  • Click "Install anyway" in the "unknown developer" popup
  • Run "zpool.exe status" to confirm it can talk to the kernel

Failure would be:

Unable to open \\.\ZFS: No error.

Success would be:

No pools available


Creating your first pool.

The basic syntax to creating a pool is as below. We use the pool name "tank" here as with Open ZFS documentation. Feel free to pick your own pool name.

# zpool create [options] tank disk
  - Create single disk pool

# zpool create [options] tank mirror disk1 disk2
  - Create mirrored pool ("raid1")

# zpool create [options] tank raidz disk1 disk2 disk3 .... diskn
  - Create raidz ("raid5") pool of multiple disks

The default options will "mostly" work in Windows, but for best compatibility should use a case insensitive filesystem.

The recommended options string for Windows is currently:

zpool create -O casesensitivity=insensitive -O compression=lz4 \
     -O atime=off -o ashift=12 tank disk
  • Creating filebased pools would look like:
# fsutil file createnew C:\poolfile.bin 200000000
# zpool.exe create tank \\?\C:\poolfile.bin

Note that "\\?\C:\" needs to be escaped in bash shell, ie

        TEST                   ONLINE       0     0     0
        \??\C:\poolfile.bin  ONLINE       0     0     0
  • Creating a HDD pool

First, locate disk name

# wmic diskdrive list brief
VMware, VMware Virtual S SCSI Disk Device  \\.\PHYSICALDRIVE2  VMware, VMware Virtual S SCSI Disk Device  0           5362882560
# zpool create tank \\.\PHYSICALDRIVE2

Exporting the pool

If you have finished with ZFS, or want to eject the USB or HDD that the pool resides on, it must first be exported. Similar to "ejecting" a USB device before unplugging it.

# zpool export tank