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I just got a mail from Linode saying that my account "has exceeded the notification threshold (1000) for disk io rate by averaging 1017.36 for the last 2 hours. "

My question is just out of curious: From the literal meaning, disk io rate must mean the rate of read/write to the server's disk. But because I've never got any notification like this during the past few years, I am interested in knowing what has caused this and what it has to do with my website.

Does pageview generate disk i/o? Does download generat disk i/o? Or only literally copying or creation of files generate it? And is it related to my website's overall performance and popularity?

I just want a brief introcution so I can research further by myself, detailed explanation is appreciated but not necessary.

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    • Check to see if you're getting a lot of SSH login attempts by running lastb - this was causing additional IO load for me. After changing to a non-standard port on the server, the IO dropped. (And so did the hacking attempts.)

Those messages you get from Linode are not warnings - they're in response to user-configurable thresholds for resource utilization. While these notifications do not necessarily mean that anything is wrong on your VM or that you need to change anything, a sudden increase in IO/CPU/etc. can be indicative of something going awry, so you'll need to dig into your logs to make sure that you can identify the source of the additional IO load.

Regarding your larger questions about IO: anything that touches the disk (either reads or writes) is considered IO. Page views will surely cause IO from writing log files, but it's likely that the php/mysql data needed to build the pageview are already cached in RAM, so they won't necessarily cause IO.

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    • > Page views will surely cause IO from writing log files, - yes, but not "A page view" as log files are going to be buffered.

Any read or write operation generates IO. As does swapping. Do free -m to see if you are using swap, if you are get more RAM or reduce your RAM usage. Also page loads read from the disk, so yes it generates IO, a good work around is to use memcached.

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