hw_disk_bus: scsi for kubernetes images

[linwalth]

I have found through some digging that the use of virtio as hw_disk_bus is not needed anymore.

(see osism/openstack-image-manager#482)

so these parameters can be set to scsi (as scsi appears to be slightly more perfomant, allowing for DISCARD [fstrim].)

https://github.com/osism/openstack-image-manager/blob/main/etc/images/kubernetes.yml#L15

https://github.com/osism/openstack-image-manager/blob/main/etc/images/gardenlinux.yml#L14

[artificial-intelligence]

I'd be really hesitant to switch the default here and would like to see actual current numbers that scsi is more performant.

as said elsewhere already: virtio-blk does support discard.

[artificial-intelligence]

So, i quickly re-researched the performance topic and so far I mostly found sources in favor of virtio-blk when it comes to performance:

• https://www.qemu.org/2021/01/19/virtio-blk-scsi-configuration/ says virtio-blk is faster than scsi (the test cited is random read 4k)
• the above source also notes, that scsi passthrough was disabled in the 5.6 kernel and replaced by virtio-scsi
• https://stackoverflow.com/a/45487683 mentions also, like the above source, that virtio-scsi is more complex code and thus slower; but it also contains the old information that virtio-scsi does support TRIM, which virtio-blk also supports.
• finally there is this blog from 2017 which has the most datapoints and tests running fio. most datapoints here are in favor of virtio-blk speed as well.

:edit: this all being said, this research is really just a few minutes of googling around so it might be very well possible this information is outdated so I'd be interested in learning of newer sources that disprove the above.

[berendt]

Please take to an SCS meeting an discuss there.

[artificial-intelligence]

@linwalth can you check if virtio-blk works for you in terms of discard? do you see any performance difference - positive or negative - for your workload?

I don't know your platform/usecase, as I'm still a little new here around 😄

If you have a problem with the current value or if you can show data that scsi works better for your usecase, we could discuss switching this again.

Thanks!

[artificial-intelligence]

@berendt I added the topic to the agenda, I hope it's okay this way:

https://input.scs.community/#2023-05-17

[fkr]

https://input.scs.community/#2023-05-17

that link is kaput ;)

Where did you add it?

[artificial-intelligence]

yeah, the markdownlinks are somehow defect, it's here (deeplinks seem to be broken somehow):

https://input.scs.community/2023-scs-team-iaas

[linwalth]

@linwalth can you check if virtio-blk works for you in terms of discard? do you see any performance difference - positive or negative - for your workload?

@artificial-intelligence I was just passing this issue down, I have no immediate contact with the usecase itself.