Tag Archives: macos

ZFS Compatibility

The best free filesystem on Earth – ZFS – also often named OpenZFS recently – has also become very portable in recent years of its development. The OpenZFS Distributions page lists 6 (six) operating systems already.

They are:

  • FreeBSD
  • Illumos
  • Linux
  • MacOS
  • NetBSD
  • Windows

… but if you would like to create a ZFS pool compatible with all of them … which options and ZFS features should you choose? There is OpenZFS Feature Flags page dedicated exactly to that topic.


These are the ones that have yes value in all operating systems.

  • async_destroy
  • bookmarks
  • empty_bpobj
  • enabled_txg
  • filesystem_limits
  • lz4_compress
  • hole_birth
  • multi_vdev_crash_dump
  • spacemap_histogram

I would also include these as only older NetBSD 4.0.5 version does not support them – but they are supported in newer NetBSD 5.3 version.

  • embedded_data
  • large_blocks
  • sha512
  • skein

There is also a dedicated zpool-features(7) man page for that information on the OpenZFS page and also zpool-features(7) man page on the FreeBSD page.

On the FreeBSD system the /usr/share/zfs/compatibility.d directory has files with supported ZFS Feature Flags for many major operating systems and ZFS versions.

% ls /usr/share/zfs/compatibility.d

Unfortunately it misses NetBSD and Illumos systems for example … but having information from the OpenZFS Feature Flags page we can find Feature Flags set that will be supported everywhere.

Here are the stats for supported ZFS Feature Flags. The higher the number the more operating systems and ZFS version it covers.

% grep -h '^[^#]' /usr/share/zfs/compatibility.d/* \
    | sort -n \
    | uniq -c \
    | sort -n
   2 draid
   5 bookmark_written
   5 device_rebuild
   5 livelist
   5 log_spacemap
   5 redacted_datasets
   5 redaction_bookmarks
   5 zstd_compress
   9 allocation_classes
   9 bookmark_v2
   9 project_quota
   9 resilver_defer
  10 edonr
  10 encryption
  11 large_dnode
  11 userobj_accounting
  18 spacemap_v2
  20 device_removal
  20 obsolete_counts
  20 zpool_checkpoint
  31 sha512
  31 skein
  32 multi_vdev_crash_dump
  36 filesystem_limits
  36 large_blocks
  37 embedded_data
  37 enabled_txg
  37 extensible_dataset
  37 hole_birth
  37 spacemap_histogram
  38 async_destroy
  38 empty_bpobj
  38 lz4_compress

As the GNU GRUB is very outdated when it comes to ZFS support it should be pretty bulletproof to use it as a starting point of limited ZFS Feature Flags support.

% cat /usr/share/zfs/compatibility.d/grub2
# Features which are supported by GRUB2

To make sure we are compatible we will now cross-link the GNU GRUB data.

First we will ‘generate’ the grep(1) command arguments that we will use in the next command.

% grep '^[^#]' /usr/share/zfs/compatibility.d/grub2 \
  | while read I
      echo "-e ' ${I}' \\"
-e ' async_destroy' \
-e ' bookmarks' \
-e ' embedded_data' \
-e ' empty_bpobj' \
-e ' enabled_txg' \
-e ' extensible_dataset' \
-e ' filesystem_limits' \
-e ' hole_birth' \
-e ' large_blocks' \
-e ' lz4_compress' \
-e ' spacemap_histogram' \

Lets now use these arguments to filter the ZFS features.

% grep -h '^[^#]' /usr/share/zfs/compatibility.d/grub2/* \
    | sort -n \
    | uniq -c \
    | sort -n \
    | grep -e ' async_destroy' \
           -e ' bookmarks' \
           -e ' embedded_data' \
           -e ' empty_bpobj' \
           -e ' enabled_txg' \
           -e ' extensible_dataset' \
           -e ' filesystem_limits' \
           -e ' hole_birth' \
           -e ' large_blocks' \
           -e ' lz4_compress' \
           -e ' spacemap_histogram' \
    | wc -l

% grep -h '^[^#]' /usr/share/zfs/compatibility.d/grub2 | wc -l

So if seems that GRUB list of ZFS Feature Flags seems pretty compatible.

Lets now cross-reference that GRUB data with the data from the OpenZFS Feature Flags page.

I will create new /usr/share/zfs/compatibility.d/OZFF file that has these ZFS Feature Flags as content.

% cat /usr/share/zfs/compatibility.d/OZFF

% wc -l /usr/share/zfs/compatibility.d/OZFF

So there are 11 GRUB ZFS Feature Flags and 13 OpenZFS ‘Compatible’ Feature Flags.

Lets see how it they compare.

% cat /usr/share/zfs/compatibility.d/OZFF \
    | grep -e async_destroy \
           -e bookmarks \
           -e embedded_data \
           -e empty_bpobj \
           -e enabled_txg \
           -e extensible_dataset \
           -e filesystem_limits \
           -e hole_birth \
           -e large_blocks \
           -e lz4_compress \
           -e spacemap_histogram \
    | wc -l

I expected 11 here instead of 10 … we will not have to compare GRUB results to the OpenZFS Feature Flags section.

% grep -h '^[^#]' /usr/share/zfs/compatibility.d/{grub2,OZFF} \
    | sort -n \
    | uniq -c \
    | sort -n
   1 extensible_dataset
   1 multi_vdev_crash_dump
   1 sha512
   1 skein
   2 async_destroy
   2 embedded_data
   2 empty_bpobj
   2 enabled_txg
   2 filesystem_limits
   2 hole_birth
   2 large_blocks
   2 lz4_compress
   2 spacemap_histogram

Seems that we finally got our 10 most compatible OpenZFS Feature Flags set.

Its this set:

  • async_destroy
  • bookmarks
  • embedded_data
  • empty_bpobj
  • enabled_txg
  • filesystem_limits
  • hole_birth
  • large_blocks
  • lz4_compress
  • spacemap_histogram

To make it more comfortable to use we will put them it into the separate /usr/share/zfs/compatibility.d/COMPATIBLE file.

# cat /usr/share/zfs/compatibility.d/COMPATIBLE

Lets now try to make that best effort most-compatible ZFS pool.

I will use one of my scripts – mdconfig.sh – to easy manipulate md(4) memory disks on FreeBSD.

# truncate -s 1g FILE
# mdconfig.sh -c FILE
IN: created vnode at /dev/md0
# zpool create -o compatibility=COMPATIBLE compatible /dev/md0
# zpool list
compatible   960M   116K   960M        -         -     0%     0%  1.00x    ONLINE  -
zroot        118G  48.6G  69.4G        -         -    36%    41%  1.00x    ONLINE  -

Now lets see what is zpool upgrade command showing us.

# zpool upgrade
This system supports ZFS pool feature flags.

All pools are formatted using feature flags.

Some supported features are not enabled on the following pools. Once a
feature is enabled the pool may become incompatible with software
that does not support the feature. See zpool-features(7) for details.

Note that the pool 'compatibility' feature can be used to inhibit
feature upgrades.


There are LOTS of ZFS Feature Flags to be activated but if we want to have our ZFS pool keep compatible – we will have to stay away from it πŸ™‚


You may get impression that you miss a lot … but you do not miss that much. Here are the ZFS Feature Flags you can fully utilize.

# zpool get all compatible | grep -v disabled
NAME        PROPERTY                       VALUE                          SOURCE
compatible  size                           960M                           -
compatible  capacity                       0%                             -
compatible  altroot                        -                              default
compatible  health                         ONLINE                         -
compatible  guid                           5395735446052695775            -
compatible  version                        -                              default
compatible  bootfs                         -                              default
compatible  delegation                     on                             default
compatible  autoreplace                    off                            default
compatible  cachefile                      -                              default
compatible  failmode                       wait                           default
compatible  listsnapshots                  off                            default
compatible  autoexpand                     off                            default
compatible  dedupratio                     1.00x                          -
compatible  free                           960M                           -
compatible  allocated                      116K                           -
compatible  readonly                       off                            -
compatible  ashift                         0                              default
compatible  comment                        -                              default
compatible  expandsize                     -                              -
compatible  freeing                        0                              -
compatible  fragmentation                  0%                             -
compatible  leaked                         0                              -
compatible  multihost                      off                            default
compatible  checkpoint                     -                              -
compatible  load_guid                      17463015630652190527           -
compatible  autotrim                       off                            default
compatible  compatibility                  COMPATIBLE                     local
compatible  feature@async_destroy          enabled                        local
compatible  feature@empty_bpobj            enabled                        local
compatible  feature@lz4_compress           active                         local
compatible  feature@spacemap_histogram     active                         local
compatible  feature@enabled_txg            active                         local
compatible  feature@hole_birth             active                         local
compatible  feature@extensible_dataset     enabled                        local
compatible  feature@embedded_data          active                         local
compatible  feature@bookmarks              enabled                        local
compatible  feature@filesystem_limits      enabled                        local
compatible  feature@large_blocks           enabled                        local

You get the very decent LZ4 compression and also ZFS Bookmarks feature which are very useful feature for sync|recv mechanism.

Keep in mind that the -o compatibility= switch for zpool(8) is available on OpenZFS 2.1 or newer. The 2.1 version is already available on the FreeBSD 13.1-BETA* releases and will be part of the FreeBSD 13.1-RELEASE systems. To make use of it on older FreeBSD releases you will have to use openzfs and openzfs-kmod packages and also use the following settings in the /boot/loader.conf file.

From that one:


Into that one:


With these openzfs and openzfs-kmod packages and above settings in the /boot/loader.conf file you can use this OpenZFS 2.1 on FreeBSD 12.2 – on FreeBSD 12.3 – and on FreeBSD 13.0 … and of course on upcoming FreeBSD 13.1 release.

Not sure if I should have add anything more here. Feel free to remind me in the commends πŸ™‚


My FreeBSD Story

As Roman Zolotarev asked if I would write an entry for his Tell Your BSD Story page I could not refuse. That page was available at the https://www.bsdjobs.com/people/hi.html URL but seems that Roman abandoned the bsdjobs.com domain unfortunately. I really tried to make it short and small but I guess its not that straight πŸ™‚

My first devices/computers/consoles (not at the same time) that I remember were Atari 2600 and Pegasus console which was hardware clone of the Nintendo NES.


Back then I did not even knew that it was Atari 2600 as I referred to it as Video Computer System … and I did not even knew any english by then. It took me about two decades to get to know (by accident) that this Video Computer System was Atari 2600 πŸ™‚

This equipment was used for playing computer games only.

Then I got AMIGA 600 computer (or should I say my parents bought it for me) which served both for playing computer games and also other activities for the first time. AMIGA is the computer that had the greatest influence on me, as it was the first time I studied the books about Amiga Workbench operating system and learned commands from Amiga Shell terminal. I loved the idea of Ram Disk icon/directory on the desktop that allowed me to transparently put any things in system memory. I still miss that concept on today’s desktop systems … and I still remember how dismal I was when I watched Amiga Deathbed Vigil movie.


At the end of 1998 I got my first PC that of course came with Windows and that computer served both as gaming machine and as well as typical tool. One time I dig into the internals with Windows Registry (which left me disgusted by its concepts and implementation) and its limited command line interface provided by CMD.EXE executable. I remember that the heart of this box was not the CPU or the motherboard but the graphics accelerator – the legendary 3Dfx Voodoo card. This company (3Dfx) – their attitude and philosophy – also left solid fingerprint on my way. Like AMIGA did.

Hence how the top of my laptop looks like now πŸ™‚


Some games was even released as special edition with the only feature being support for the 3Dfx Glide driver like Need for Speed II: Special Edition.


After ‘migration’ from AMIGA to PC it never again ‘felt right’. The games were cool but the Windows system was horrible. Time has passed and different Windows versions and hardware modifications took place. Windows XP felt really heavy at that time, not to mention Windows 2000 for example with even bigger hardware requirements. I also do not understand all the hate about Windows ME. It crashed with the same frequency as Windows 98 or later Windows 98 Second Edition but maybe my hardware was different πŸ™‚


I do not have any ‘mine’ screenshots from that period as I lost all my 40 GB (huge then) drive of data when I moved/resized the partition with Partition Magic to get some more space from the less filled C: drive. That day I learned hard that “there are people who do backups and people who will do backups”. I never lost data again as I had multiple copies of my data, but the same as Netheril fall the lost data was was gone forever.

I always followed various alternatives which led me to try Linux in 2003, after reading about various distributions philosophies I decided to run Slackware Linux with KDE 3. My buddy used Aurox Linux by then (one of the few Linux distributions from Poland) and encouraged me to do the same – especially in the context of fixing possible problems as he already knew it and also as he recently dumped Windows system. But Slackware sounded like a better idea so I took that path instead. At first I dual booted between Windows XP and Slackware Linux cause I had everything worked out on the Windows world while I often felt helpless in the Linux world, so I would reboot into Windows to play some games or find a solution for Linux problem if that was required. I remember how strange the concept of dual clipboards (PRIMARY and SECONDARY) was for me by then. I was amazed why ‘so much better’ system as Linux (at least marketed that way) needs a system tray program to literally manage the clipboard. On Windows it was obvious, you do [CTRL]+[C] to copy and [CTRL]+[V] to paste things, but on Linux there (no I know its X11 feature) there were two clipboards that were synchronized by this little system tray program from KDE 3. It was also unthinkable for me that I will ‘lost’ contents of last/recent [CTRL]+[C] operation if I close the application from which the copy was made. I settled down a little on Slackware but not for long. I really did not liked manual dependency management for packages for example. Also KDE 3 was really ugly and despite trying all possible options I was not able to tweak it into something nice looking.

After half a year on Slackware I checked the Linux distributions again and decided to try Gentoo Linux. I definitely agree with the image below which visualizes Gentoo Linux experience, especially when You install it for he first time πŸ™‚


Of course I went with the most hardcore version with self building Stage 1 (compiler and toolchain) which was horrible idea at that time because compilation on slow single core machine took forever … but after many hours I got Gentoo installed. I now have to decide which desktop environment to use. I have read a lot of good news about Fluxbox at that time so this is what I tried. It was very weird experience (to create everything in GUI from scratch) but very pleasant one. That recalled me the times of AMIGA … but Linux came in the way too much often. The more I dig into Gentoo Linux the more I read that lots of Gentoo features are based on FreeBSD solutions. Gentoo Portage is a clone of FreeBSD Ports. That ‘central’ /etc/rc.conf system configuration file concept was taken from FreeBSD as well. So I started to gather information about FreeBSD. The (then) FreeBSD website or FreeBSD Ports site (still) felt little outdated to say the least but that did not discouraged me.

Somewhere in 2005 I installed FreeBSD 5.4 on my computer. The beginnings were hard, like the earlier step with Gentoo but similarly like Gentoo the FreeBSD project came with a lot of great documentation. While Gentoo documentation is concentrated within various Gentoo Wiki sites the FreeBSD project comes with ‘official’ documentation in the form of Handbook and FAQ. I remember my first questions at the now nonexistent BSDForums.org site – for example one of the first ones – how to scroll the terminal output in the plain console. I now know that I had to push Scroll Lock button but it was something totally new for me.

How BSDForums.org looked like.


This is the earliest screenshot I got from that period, and Gentoo setup looked very similar.


Why FreeBSD and not OpenBSD or NetBSD? Probably because Gentoo based most their concepts on the FreeBSD solutions, so that led me to FreeBSD instead of the other BSD operating systems. Currently I still use FreeBSD but I keep an steady eye on the OpenBSD, HardenedBSD and DragonFly BSD solutions and improvements.

As the migration path from Linux to FreeBSD is a lot easier – all configuration files from /home can be just copied – the migration was quite fast easy. I again had the Fluxbox configuration which I used on the Gentoo. Now – on FreeBSD – it started to fell even more like AMIGA times. Everything is/has been well thought and had its place and reason. The documentation was good and the FreeBSD Community was second to none.

I even decided to upgrade the hardware to something more exotic. I got Gigabyte-GA-7DPXDW server motherboard with dual CPU sockets – and as Athlon XP (desktop) processors were very easily modified to ‘be’ Athlon MP (server) ones I got also the second one along with 1 GB of ECC RAM.


This dual CPU setup – quite unusual at these times – server me very well. I switched from nvidia binary blob driver to software but open nv because nvidia would break my uptime every several days πŸ™‚

I accumulated 30 days of uptime on that desktop box, not bad for a system without any emergency UPS πŸ™‚


This was also the last time I used ECC RAM on FreeBSD (at least on my boxes) while ZFS did not even existed on FreeBSD πŸ™‚ But as time flied I started to feel the need for something faster. As I also got interested in Intel graphics card I got the new motherboard with fastest Intel graphics card available then – as silly as it sounds – the Asus P5B-V with Intel X3000 GMA … and that was a terrible idea because FreeBSD graphics stack supported all the Intel graphics cards instead of that one. At the beginning I used software vesa driver but the problem was not the performance of the driver (as I also had quad core Intel Q6600 CPU) but the resolution on the screen. As I got 1280 x 1024 screen by then using limited 1024 x 768 was real PITA. I decided that I will try something else then FreeBSD will Intel X3000 support finally arrives. I needed to do something fast as I also needed to write my Masters Thesis at that time.

That was in the middle of 2007. I wanted to try the other end of the Linux distributions spectrum. Ubuntu. I could not go more ‘desktop’ way πŸ™‚ It of course installed gently with GNOME 2 environment and pulseaudio already unfortunately existed. As I preferred to run my computer all the time back then (I did not payed the electricity bills) there were several things that annoyed my very much. For example the mentioned pulseaudio – the sound freezed after one-two days of using the computer (even if I did not played any music or videos) and it stayed that way. I could restart pulseaudio or reload the ALSA modules but it stayed in this SUSFU state (situation unchanged still fucked up) until reboot. As I needed to finish my Masters Thesis I did not had time to reinstall into something else as pulseaudio will be probably similarly broken on other Linux distributions and FreeBSD was still lacking the Intel X3000 GMA support. Generally GNOME 2 experience was not bad but I really missed all my custom settings, keyboard shortcuts and customized behavior. I remained in pain on the Ubuntu for two months – to the time I have finished my Masters Thesis about Operating Systems’ Virtualization which you can download and read but its in Polish so use translator if needed πŸ™‚

This is how Ubuntu looked back then.


I also had ‘side’ journey to the Mac wonderland as I got opportunity to use Macbook Pro with Mac OS X Leopard for a year. That allowed me to get real ‘feel’ of the Mac ecosystem and their hardware (and philosophy) so I will not repeat same stereotypes over and over again like a lot of anti-apple people. But after I switched back to FreeBSD system at work it just felt better. I used Terminal.app on Mac a lot but the xterm(1) at FreeBSD just felt more natural.

What makes me laugh now that I created Mac styled Fluxbox themes years till I got to run Mac and I still like Mac OS X look from the Leopard times.


There was time on which I also played with Solaris (and later OpenSolaris). I must admit that there was time when Solaris so called Java Desktop based on GNOME 2 was really looking good. It was so good that only Mac OS X could only rival it for the best looking os by then.


I really liked Solaris concepts and solutions like Zones and ZFS, also Crossbow, Comstar or IPS (FreeBSD did not had PNGng by then). But I always got problem with ‘desktop’ software. While I had everything in the FreeBSD Ports – almost the same amount of applications that is available on Linux – there was always some applications lacking in the Solaris world.

The Solaris ‘journey’ also left print on my soul so my Fluxbox themes went into Solaris style πŸ™‚


After the Ubuntu fiasco I got other motherboard as FreeBSD still did not supported Intel GMA X3000 card and settled in the FreeBSD land again. What a relief it was after this pulseaudio nonsense. In the meantime as I read a lot of good experiences about Openbox I decided to try it out instead of Fluxbox. It was strange feeling to mess with XML configuration files at the beginning but as I got used to it and ordered the rc.xml and menu.xml configuration files properly it was not a problem. Since then I used FreeBSD on different machines including physical servers, virtual machines and laptops. I learned that adequate supported hardware is the most important factor in FreeBSD ecosystem.

I still use Openbox and still use FreeBSD today and my desktop looks like that one below.


After 15 years of using various Windows, UNIX (macOS/AIX/HP-UX/Solaris/OpenSolaris/Illumos/FreeBSD/OpenBSD/NetBSD) and UNIX-like (Linux) systems I always come to conclusion that FreeBSD is the system that sucks least. And sucks least with each release and one day I will write why FreeBSD is such great operating system … if I already haven’t πŸ™‚


As Roman Zolotarev got a moment he added my story to his Tell Your BSD Story page. That page was available at the https://www.bsdjobs.com/people/ URL but seems that Roman abandoned the bsdjobs.com domain unfortunately.

Thanks Roman!

You may check it for yourself at Slawomir Wojciech Wojtczak (vermaden) runs FreeBSD page.