IO rate on Xen; I don't quite get it
Now I'm on Xen, and I enabled e-mail alerts for my node. IO rate alert was triggered for me , yesterday:
Your Linode has exceeded the notification threshold for disk io rate by averaging 620.49 for the last 2 hours.
How is disk io rate calculated?
How does the token limiter work for Xen guests?
Where can I see what my limit is? (I have a Linode 720)
i.e. How do I determine if I care about this alert that was triggered?
I think that UML was io requests and Xen is blocks of io. I think in another post caker recommended quadrupling the alert threshold. I could be wrong though. I'd look around the forum.
Each count for calculating disk i/o is an i/o operation issued by your Linode. The default level for triggering an alert is 100 ops/sec (average over two hours) - compared with the 512 tokens per second refill rate under UML. Most Linodes operate the the 0 - 10 i/o ops per second range (averaged).
Your alert is not the end of the world but you probably want to see what your Linode was doing at that time - in case unusual activity is a warning of trouble to come. Linking big libraries is the only thing that really gets my i/o rate up.
An IO request could contain more than one block, so you probably want to increase your IO alert threshold under Xen.