What is IO delay?


Active Member
Jun 24, 2019
I am new to proxmox and want to understand it better. A node shows me the "IO delay" value. What is IO delay? How is it calculated? Knowing this would make it easy to answer questions like: what IO delay is acceptable? Is 5% a high value or is 50% acceptable? etc.

I tried searching the documentation and found nothing on what it is. Google and forum searches give me hundreds of pages where people discuss how to reduce it, or what is causing it, but nothing on what this value actually means.

Related question: having a node with mixed storage, e.g., SSDs, HDDs or even CEPH or other networked storages. How does the storage type ifluences the IO delay value?
io delay is simple the 'iowait' metric of the linux kernel, which values are ok is very dependent on your config and situation,

there are many pages which describe what it is, e.g. the man page of iostat(1) says the following:

Show the percentage of time that the CPU or CPUs were idle during which the system had an outstanding disk I/O request.
  • Like
Reactions: masgo
Geat, thanks! I know %iowait and iostat.

Would be nice if proxmox called it this way or included some mouse-over hint to it or at least something in the manual when I click the "help" button.

As a suggestion: a different metric for IO might be better. %iowait can be highly missleading, especially when comparing different CPUs and especially when multiple process are running on the cpu. Maybe something comparable to the device-based output of iostat? In my experience looking at tps and read/write speeds usually helped me find a problem much faster than %iowait.
  • Like
Reactions: rschrem


The Proxmox community has been around for many years and offers help and support for Proxmox VE, Proxmox Backup Server, and Proxmox Mail Gateway.
We think our community is one of the best thanks to people like you!

Get your subscription!

The Proxmox team works very hard to make sure you are running the best software and getting stable updates and security enhancements, as well as quick enterprise support. Tens of thousands of happy customers have a Proxmox subscription. Get yours easily in our online shop.

Buy now!