Default setting of SCSI controller is now VirtIO SCSI-Single

[hbdy]

I saw in the release notes of PVE 7.3 that the default setting for new VMs now provides that IO threads is enabled and thus VirtIO SCSI-Single is selected as controller instead of VirtIO SCSI before.

I have three questions about this:

a) What is the advantage or reason for changing the default setting?

b) Does it make any difference for VMs which have only one disk?

c) Should I change old VMs to VirtIO SCSI single?

 

[leesteken]

b) Does it make any difference for VMs which have only one disk?

It can if you enabled IO Thread on the virtual disk. Some virtual devices need to be emulated and even paravirtualized devices (VirtIO) require some kind of processing. The new default allows disk I/O to be done in a separate thread compared to those (and other disks). If your system has many but not very fast cores, it could really help and it should not hurt performance anyway.

 

[bbgeek17]

We've done some performance qualification of various options and our conclusion prior to recent change in PVE was:

Parameter	Description	Default In 7.2	Recommended Setting
SCSI Controller	SCSI emulation driver type	n/a	scsi-virtio-single
AIO Type	System interface used to Asynchronous I/O	io_uring	native
IOThreads	Provides dedicated threads for disk I/O	disabled	enabled

https://kb.blockbridge.com/technote/proxmox-aio-vs-iouring/

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