Recently I switched my media server from ext4 on LVM to ZFS. This has mostly been a great success, however I noticed a big problem with MythTV. In the past it would take 1-2sec to start playing video, now it would take 5-60sec. Ouch!
In this post I’ll describe the trouble-shooting techniques I applied, along with all the various things I found and fixed along the way. If you just want to see the solution you can scroll to the end.
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What is asynchronous I/O?
The web services I build spend most of their time doing one of these two classes of things:
- Processing – Burning CPU cycles calculating things. For example JSON parsing, HTML rendering, image processing, etc.
- I/O – Waiting for some event external to the CPU/RAM system to finish. For example an HTTP request or DNS request.