Application (Steam Game) error when starting from ZFS dataset without its own drive letter assigned

[besterino]

I decided to give ZFS a long term real life test on my main Windows machine. Admittedly I mainly use it for games, but that should at least give a quite broad variety of test applications, possibly also with a certain variety of how applications access storage...

Current Setup / ZFS layout:

1. One (basic) pool over 2 NVME Gen4 SSD: "nvme"
2. One dataset on pool nvme: "games"

For Steam I created a folder "SteamLibrary" on the dataset "games", which is setup in Steam as the default library location.

If I assign a drive letter only to the pool and point Steam to the "SteamLibrary"-Folder on the Dataset, the game Pax Dei won't start with an error message. If i assign a drive letter (only) to the dataset and point Steam to the exact same Folder, the game starts normally.

Note: The second game I tested so far (Icarus) starts fine, even if only the Pool has a drive letter. I can only guess that is has something to do with either (i) how Pax Dei (and maybe other applications?) access storage, or (ii) the anti-cheat tool required to be running for Pax Dei called "EasyAntiCheat".

EDIT: I used OpenZFSOnWindows-debug-2.3.0rc6g

[tribals]

I've noticed the same thing on some applications I'm trying to exec from ZFS datasets.

I've tried your solution, that is: assign driveletter to tank/games and remove it from root dataset. Unfortunately, that didn't work for apps I'm trying to launch. Then I decided to revert all this back, and assigned - to tank/games, and Z to tank. Now I've tank in tank, and property source is shown as "local" instead of "default" as it was:

C:\> zfs get driveletter tank
NAME  PROPERTY     VALUE        SOURCE
tank  driveletter  Z            local

C:\> zfs get driveletter tank/games
NAME        PROPERTY     VALUE        SOURCE
tank/games  driveletter  -            local

zfs history for the sake of clarity:

C:\> zpool history
History for 'tank':
2025-06-30.00:25:03 zpool create -O normalization=formD -O compression=lz4 -O atime=off -o ashift=12 -O driveletter=Z -O acltype=posix -O xattr=sa -O utf8only=on tank \\?\Harddisk0Partition4
2025-06-30.00:25:33 zfs create tank/games
2025-10-01.23:45:07 zfs create tank/tmp
2025-12-10.14:10:41 zfs set driveletter=G tank/games
2025-12-10.14:20:21 zfs set driveletter=- tank/games
2025-12-10.14:24:19 zfs set driveletter=G tank/games
2025-12-10.14:24:31 zfs set driveletter=off tank
2025-12-10.14:25:06 zfs set driveletter=- tank/games
2025-12-10.14:25:32 zfs set driveletter=Z tank

As you can see, I've tank/tmp also, and it's driveletter looks like this:

C:\ zfs get driveletter tank/tmp
NAME      PROPERTY     VALUE        SOURCE
tank/tmp  driveletter  -            default

Could it be restored to "default" for tank/games and tank itself? I'm not sure if it affects anything, but that way I would be calmer. I've tried zfs inherit but it told me that "driveletter cannot be inherited".

@lundman cold you please take a look?

[lundman]

If you just want to restore it, i believe the command is inherit. As in zfs inherit driveletter tank/tmp

[tribals]

I've tried inherit with no luck.

That's minor issue - the real one is that I'm still not able to launch some applications from ZFS.

😢

[lundman]

We did fix a deadlock with read/writes last week, although waiting to hear back on it. Feel free to test that special build though, see if it improves things for you