[thesz]

Yes, the file system appears to be Windows one.

I remember no questions being asked when I set up WSL2.

I really doubt that WSL2 will be at native speed with the Linux file system, because reads and writes still have to go through Windows kernel to be mapped into actual hardware reads/writes.

[sz4kerto]

> I really doubt that WSL2 will be at native speed with the Linux file system, because reads and writes still have to go through Windows kernel to be mapped into actual hardware reads/writes.

No, Linux is running alongside Windows, not under it. Windows itself is virtualized when WSL2 is turned on, and both Linux and Windows run under Hyper-V. It's quite fancy actually.

[madeofpalk]

> Windows itself is virtualized when WSL2 is turned on

Is there documentation/explainer for this? I've been trying to understand more about this (was this a change in Windows 11? Is it only when WSL2 is installed?) for a while now, but not found anything apart from stray HN comments every now and then.

[wongarsu]

It's the fundamental difference between WSL1 and WSL2. As designed in the 90s, the Windows NT kernel can have different subsystems that offer different userspace APIs to different software. Originally there were the Win32 subsystem, the Security subsystem, the Posix subsystem and the OS/2 subsystem. The latter two fizzled out, but WLS1 is basically just another subsystem that provides a linux-compatible API to the Windows kernel. As it turns out providing full compatability is really hard though, so WSL2 is a complete rewrite, ignoring the subsystem concept. It basically just runs linux in Hyper-V, and adds some UI/UX to make that convinient.

That Windows is then running virtualized is just how Hyper-V works, as soon as you turn on Hyper-V the host Windows runs as a guest in Hyper-V, though with special privileges [1]

https://learn.microsoft.com/en-us/virtualization/hyper-v-on-...

[thesz]

https://github.com/microsoft/WSL/issues/2395

This is still a problem with WSL2, at least on my WSL2 with Windows file system mappings.

I tried to use instructions that use fossil from the hctree page: https://sqlite.org/hctree/doc/hctree/doc/hctree/index.html

Fossil employs sqlite to store SCM information and it fails with "SQLITE_IOERR(1290): os_unix.c:39533: (22) fsync(...)" error, which is the same with VirtualBox: https://www.fossil-scm.org/forum/forumpost/7fb6c96d80?t=c

So WSL2, having to put up with Windows quirks, is not much a Linux anymore. It is slow and some programs can't even run.

[csdvrx]

A valid critic given that there's no native filesystem support yet.

But if WSL2 is given its own drive to mount and do what it wants with it, the issue should disappear.

And when WSL2 supports passing partitions, the issue will vanish.

[joshuaissac]

> WLS1 is basically just another subsystem that provides a linux-compatible API to the Windows kernel

WSL1 is not an NT subsystem, either. WSU (the POSIX subsystem) was an actual NT subsystem, but with WSL, they abandoned this concept and went with a different design for performance reasons.

https://news.ycombinator.com/item?id=25249262

[shawnz]

WSL2 is powered by Hyper-V, which is a "type 1 hypervisor":

https://en.m.wikipedia.org/wiki/Hypervisor#Classification

https://learn.microsoft.com/en-us/windows-server/administrat...

[jmmv]

I wrote something on this topic a while ago: https://jmmv.dev/2020/11/wsl-lost-potential.html

[shawnz]

Note that WSL 1 doesn't use the NT subsystem functionality. See this sibling comment for details https://news.ycombinator.com/item?id=34640434

[wongarsu]

> I remember no questions being asked when I set up WSL2.

If the (WSL) path to your project is inside ~/ it's on the linux file system. If it's in /mnt/c/ it's in the Windows filesystem. In WSL1 those were about equally fast, both going throught the windows kernel. With WSL2, accessing /mnt/c/ from Linux has to go through Windows, and accessing \\wsl$ from Windows has to go through Linux, so where you put the files decides where they are fast.

[csdvrx]

> In WSL1 those were about equally fast, both going throught the windows kernel

Yes, WSL1 was great. I hope it will never be sunset, as I need good IO performance.

> where you put the files decides where they are fast.

I also also hope we'll eventually get an option to pass partitions to HyperV, which is currently possible only with full disks.

It would be a return to the previous WSL1 level of performance for files within a NTFS partition: even if you'd need a separate NTFS partition, that'd be a minor nuisance to guarantee performance.

[pacoverdi]

> I really doubt that WSL2 will be at native speed with the Linux file system

I had the same doubts, but when I finally took the time to install it, I found out that I was wrong. One Java program that I use, which is very heavy on the filesystem and slow like hell under Windows it a LOT faster under WSL2.

As Java profiler support is poor on Windows, I now use WSL2 to run async-profiler sessions and get results as accurate as on native Linux.

EDIT to add: you really have to run things fully in the WSL2 filesystem, be it for compiling or using a program. The performance is awful if you run WSL2 processes under the Windows filesystem.

[cercatrova]

You are incorrect in the last paragraph but that was already explained here. Try putting the files in the Linux file system and only using that.

[Kipters]

They will go through Hyper-V, not Windows