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Top-level
Sergey Kibish
Maybe disks start to die? No. S.M.A.R.T. passes and other checks do not show that something is wrong. Memory leak? Nope, all good. No app has stairway to heaven memory behaviour. Swap is being used despite not all RAM is in use and there is free even free space. Why swap is being used? 2 comments
Sergey Kibish
Now imagine performance of swap on ZFS raid array. It’s damn slow and if accessed frequently, it is very bad for performance and that’s why high iowait. So, solution was to disable swap and all numbers went back to normal and server is healthy and live happily ever after. The end |
Gregory's Server
Turns out that this version had fixed a problem where ZFS ARC cache would only use 50% of RAM on Linux, so now it tries to use as much as possible for cache and release when apps require memory.
Seems like an algorithm decides to use swap for everything else because ARC has higher priority.
Why system has swap in first place? Because by default TrueNAS creates swap of 2GB size on each disk which I left as is long time ago. But this is configurable and should be set to zero.