VirtFS is slow (20MB/s) on MacOS with Ubuntu 24.04 guest

[erikschul]

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Describe the issue

Given a shared folder on the guest:

cat /etc/fstab
...
share   /mnt/example        9p      trans=virtio,version=9p2000.L,rw,_netdev,nofail

Write performance is slow (20 MB/s). This was discovered because other applications performed very poorly.

cd /mnt/example
dd bs=1M count=256 if=/dev/zero of=test
^C
181+0 records in
181+0 records out
189792256 bytes (190 MB, 181 MiB) copied, 9.77671 s, 19.4 MB/s

Is this the expected performance?

An identical setup using VMware Fusion (and their shared folder implementation, fuse.vmhgfs-fuse) has a speed of 1.1 GB/s.

Configuration

• UTM Version: 4.5.3
• macOS Version: 14.5
• Mac Chip (Intel, M1, ...): M1 Pro

Crash log

Debug log

Upload VM

[kstlouis]

I'm seeing this too. fstab:

share   /media/Data     9p      trans=virtio,version=9p2000.L,rw,_netdev,nofail00

Test result:

bs=1M count=800 if=/dev/zero of=test status=progress
359661568 bytes (360 MB, 343 MiB) copied, 16 s, 22.5 MB/s
^C
355+0 records in
355+0 records out
372244480 bytes (372 MB, 355 MiB) copied, 16.5783 s, 22.5 MB/s

The same transfer from the host to the shared drive:

dd bs=1M count=8000 if=/dev/zero of=test status=progress
  7626293248 bytes (7626 MB, 7273 MiB) transferred 9.138s, 835 MB/s
8000+0 records in
8000+0 records out
8388608000 bytes transferred in 9.942618 secs (843702132 bytes/sec)

Is this an issue with UTM's implementation of VirtFS, or something upstream? (Also completely open to the more likely option that it's a config issue on my end 😅) My primary use case for this VM is writing to this disk array, so unless there's some kind of fix available I need to look at other options.