IDE vs SCSI

[Stefano Giunchi]

I have a client with an old installation: PVE4.4 on an OLD HP server, with HW RAID and working BBU.
Waiting to replace it, I'm trying to find ways to speed up VMs.
I saw that most of virtual disks were created with IDE controllers adn writethrough enabled, thus I thought it was an easy win to replace it with a SCSI controller.

It was not.

I tried various settings, the best one with SCSI should be writethrough enabled: but as you can see, Read performance is great but Write is abysmal.

LEFT: IDE
RIGHT: SCSI
Both with writethrough enabled



I tried to use writeback, which sould be ok to use with BBU backed HW RAID, but CyrstalDiskMark crashes consistently with that, thus I dont't trust it.

Any suggestion is welcome.

 

[Alwin]

Any suggestion is welcome.

Update/upgrade Proxmox VE and the OS inside the VM. Including the VirtIO drivers. Many improvements have been made since then.

Both with writethrough enabled

Try your tests with cache=disabled. IDE is not the best for performance.

 

[Stefano Giunchi]

Hi Alwin,thanks for your answer.

Update/upgrade Proxmox VE and the OS inside the VM. Including the VirtIO drivers. Many improvements have been made since then.

I'll push for the update.

Try your tests with cache=disabled. IDE is not the best for performance.

without cache, performance are the worst:

IDE without cache


SCSI without cache

 

[Alwin]

without cache, performance are the worst:

It works as expected, I would say. The different cache modes benefit IDE/SCSI a little differently.
https://pve.proxmox.com/wiki/Performance_Tweaks#Disk_Cache