Accessing Linux files through \\wsl$ is unbearably slow

[glen-84]

• Your Windows build number: (Type ver at a Windows Command Prompt)

Microsoft Windows [Version 10.0.18362.175]

• What you're doing and what's happening: (Copy&paste the full set of specific command-line steps necessary to reproduce the behavior, and their output. Include screen shots if that helps demonstrate the problem.)

Accessing Linux files via \\wsl$\Ubuntu, and it's super slow.

I did some basic testing with dd, and found the following:

Write in //wsl$/Ubuntu...

dd if=/dev/zero of=//wsl$/Ubuntu/home/glen/testwrite.img bs=100M count=1 oflag=dsync

• 104857600 bytes (105 MB, 100 MiB) copied, 18.186 s, 5.8 MB/s
• 104857600 bytes (105 MB, 100 MiB) copied, 17.8413 s, 5.9 MB/s

MCAFEE REMOVED:

• 104857600 bytes (105 MB, 100 MiB) copied, 16.1272 s, 6.5 MB/s
• 104857600 bytes (105 MB, 100 MiB) copied, 15.9704 s, 6.6 MB/s

dd if=/dev/zero of=//wsl$/Ubuntu/home/glen/testlatency.img bs=512 count=1000 oflag=dsync

• 512000 bytes (512 kB, 500 KiB) copied, 3.53898 s, 145 kB/s
• 512000 bytes (512 kB, 500 KiB) copied, 0.335095 s, 1.5 MB/s
• 512000 bytes (512 kB, 500 KiB) copied, 0.330495 s, 1.5 MB/s

Read in //wsl$/Ubuntu...

time dd if=//wsl$/Ubuntu/home/glen/testwrite.img of=/dev/null bs=8k

• 104857600 bytes (105 MB, 100 MiB) copied, 14.9655 s, 7.0 MB/s

real 0m15.010s
user 0m0.078s
sys 0m0.265s

• 104857600 bytes (105 MB, 100 MiB) copied, 4.20551 s, 24.9 MB/s

real 0m4.251s
user 0m0.031s
sys 0m0.124s

MCAFEE REMOVED

• 104857600 bytes (105 MB, 100 MiB) copied, 3.71398 s, 28.2 MB/s

real 0m3.781s
user 0m0.046s
sys 0m0.125s

• 104857600 bytes (105 MB, 100 MiB) copied, 3.64852 s, 28.7 MB/s

real 0m3.733s
user 0m0.030s
sys 0m0.140s

---

Write in ~...

dd if=/dev/zero of=/home/glen/testwrite.img bs=100M count=1 oflag=dsync

• 104857600 bytes (105 MB, 100 MiB) copied, 0.390321 s, 269 MB/s
• 104857600 bytes (105 MB, 100 MiB) copied, 0.371199 s, 282 MB/s

dd if=/dev/zero of=/home/glen/testlatency.img bs=512 count=1000 oflag=dsync

• 512000 bytes (512 kB, 500 KiB) copied, 0.0086376 s, 59.3 MB/s
• 512000 bytes (512 kB, 500 KiB) copied, 0.0088582 s, 57.8 MB/s
• 512000 bytes (512 kB, 500 KiB) copied, 0.0082154 s, 62.3 MB/s

Read in ~...

time dd if=/home/glen/testwrite.img of=/dev/null bs=8k

• 104857600 bytes (105 MB, 100 MiB) copied, 0.113269 s, 926 MB/s

real 0m0.128s
user 0m0.016s
sys 0m0.094s

• 104857600 bytes (105 MB, 100 MiB) copied, 0.115235 s, 910 MB/s

real 0m0.132s
user 0m0.031s
sys 0m0.109s

---

Write in /mnt/c/Users/Glen... (from distro)

dd if=/dev/zero of=/mnt/c/Users/Glen/testwrite.img bs=100M count=1 oflag=dsync

• 104857600 bytes (105 MB, 100 MiB) copied, 0.384083 s, 273 MB/s
• 104857600 bytes (105 MB, 100 MiB) copied, 0.252227 s, 416 MB/s

dd if=/dev/zero of=/mnt/c/Users/Glen/testlatency.img bs=512 count=1000 oflag=dsync

• 512000 bytes (512 kB, 500 KiB) copied, 0.0099631 s, 51.4 MB/s
• 512000 bytes (512 kB, 500 KiB) copied, 0.0116009 s, 44.1 MB/s
• 512000 bytes (512 kB, 500 KiB) copied, 0.0100696 s, 50.8 MB/s

Read in /mnt/c/Users/Glen... (from distro)

time dd if=/mnt/c/Users/Glen/testwrite.img of=/dev/null bs=8k

• 104857600 bytes (105 MB, 100 MiB) copied, 0.11045 s, 949 MB/s

real 0m0.127s
user 0m0.000s
sys 0m0.125s

• 104857600 bytes (105 MB, 100 MiB) copied, 0.109702 s, 956 MB/s

real 0m0.122s
user 0m0.000s
sys 0m0.125s

---

Write in /c/Users/Glen... (from Windows)

dd if=/dev/zero of=/c/Users/Glen/testwrite.img bs=100M count=1 oflag=dsync

• 104857600 bytes (105 MB, 100 MiB) copied, 0.351462 s, 298 MB/s
• 104857600 bytes (105 MB, 100 MiB) copied, 0.359245 s, 292 MB/s

dd if=/dev/zero of=/c/Users/Glen/testlatency.img bs=512 count=1000 oflag=dsync

• 512000 bytes (512 kB, 500 KiB) copied, 0.112353 s, 4.6 MB/s
• 512000 bytes (512 kB, 500 KiB) copied, 0.110369 s, 4.6 MB/s
• 512000 bytes (512 kB, 500 KiB) copied, 0.113078 s, 4.5 MB/s

Read in /c/Users/Glen... (from Windows)

time dd if=/c/Users/Glen/testwrite.img of=/dev/null bs=8k

• 104857600 bytes (105 MB, 100 MiB) copied, 0.0635338 s, 1.7 GB/s

real 0m0.105s
user 0m0.000s
sys 0m0.061s

• 104857600 bytes (105 MB, 100 MiB) copied, 0.0628403 s, 1.7 GB/s

real 0m0.092s
user 0m0.015s
sys 0m0.046s

TL;DR:

\\wsl$\Ubuntu

• Writing: ~6 MB/s !!!
• Reading: ~28 MB/s !!!

/home/glen

• Writing: ~275 MB/s
• Reading: ~915 MB/s

/mnt/c/Users/Glen

• Writing: ~300 MB/s
• Reading: ~950 MB/s

/c/Users/Glen (from Windows)

• Writing: ~295 MB/s
• Reading: ~1.7 GB/s

😞

• What's wrong / what should be happening instead:

It needs to be a lot faster in order to be useable.

• Strace of the failing command, if applicable: (If some_command is failing, then run strace -o some_command.strace -f some_command some_args, and link the contents of some_command.strace in a gist here).

n/a

• For WSL launch issues, please collect detailed logs.

n/a

[therealkenc]

#4197

[glen-84]

@therealkenc That issue is about WSL2, and has nothing to do with \\wsl$.

[therealkenc]

One discussion thread for 9p perf, both directions, is plenty.

[glen-84]

@therealkenc Doesn't WSL2 have a completely different architecture (using a lightweight VM)? Are you suggesting that accessing \\wsl$ in WSL1 uses exactly the same set of technologies that are used when accessing /mnt/c in WSL2?

[benhillis]

@glen-84 - Correct, \\wsl$ in WSL1 and WSL2 both use 9p. In WSL2 9p is also used for Windows drive access (/mnt/c etc).

[glen-84]

Okay, I apologize for the duplicate.

[eliecer2000]

This worked for me. for my WSL2 distro

wsl --set-version distro 1

it will take a few minutes

go back to version 2
wsl --set-version distro 2