Disk cache setting for VPS and VM

Incus
1

Hello, I’m using Incus 7.0.1 from Debian 13 (backports)

Container uses DIR storage driver and
$ incus config device set MyMachine root cache=unsafe
Error: Invalid devices: Device validation failed for “root”: Invalid device option “cache”

Machine I suppose uses qcow2 file for storage and
$ incus config device set MyContainerName root cache=unsafe
Error: Invalid devices: Device validation failed for “root”: Invalid device option “cache”

1. Is it possible to do so for containers?

2. How to I make QEMU receives cache=unsafe parameter for disk specification?

Thank you.

2

Disk devices don’t have a cache option, as the error message says. There is however an io.cache option, which is only available with virtual machines.

3 
$ incus config set MyMachine io.cache=unsafe
Error: Invalid expanded config: Unknown configuration key: io.cache
$ incus config device set MyMachine root io.cache=unsafe
Error: Failed to update device "root": Failed applying limits for disk device "root": DeviceNotFound: Device 'dev-incus_root' not found
$ incus config device show MyMachine
eth0:
  host_name: MyMV-eth0
  ipv4.address: 192.168.2.12
  network: MyBridge1
  type: nic
root:
  path: /
  pool: local
  size: 50GiB
  type: disk

(It’s using disk image file, and QEMU allows cache=unsafe specification for this)

4 
$ incus config set MyMachine io.cache=unsafe
Error: Invalid expanded config: Unknown configuration key: io.cache

The option only applies to devices, not instances as a whole.

$ incus config device set MyMachine root io.cache=unsafe
Error: Failed to update device "root": Failed applying limits for disk device "root": DeviceNotFound: Device 'dev-incus_root' not found

Well that one’s weird, does that ring any bell, @stgraber?

5

That’s something we fixed in 7.3 I believe.

6

Oh, could that fix be backported to LTS version please?

7

It most likely has already been, we process backports every week, but LTS only releases every 3 months or so, so you’ll need to wait for 7.0.2 for the fix.