I’ve got a couple of VMs and a container running on my NAS, and when I looked at the Resource Monitor, I was surprised to see it using 11GB of swap—even though it’s only tapping into 34.5GB of RAM.
My instinct tells me the NAS shouldn’t be swapping anything, and definitely not to the volume—it’s a spinning disk, not an SSD, so that feels inefficient.
I’ve just started using LibreNMS to keep an eye on my NAS, and here’s what the memory usage has looked like since the last reboot.
Does anyone know why my NAS is using such a large amount of swap space? Is this expected behavior, or something I should be concerned about? I’d appreciate hearing your experiences.
First of all, I would love to hear more about your experiences with LibreNMS was I’ve been considering installing it.
Second, I think QNAP must swap un-needed system resources to disk in order to keep memory free for applications or other uses as needed. Images from my two big NAS units are below. The first has 64GB of memory. I’m using half that right now but I’m still using 12GB of swap. The second NAS has 32GB but I’ using 12GB there as well. Given the fact that my two NAS units and yours are all running roughly around the same level of swap, I’ve got a feeling that it’s certainly OS resource related.
This is how Linux works. Caches are good for I/O performance, and some memory data are quite cold. Linux will try to move out the recently-unused part to give more room to the hot part. So, if you do heavy I/O and run a lot of passive apps (having their memory untouched for a long time), Linux will swap out those unused memory pages. They will not go back until they’re accessed.
As long as your IO load is acceptable you don’t meed to worry about high swap usage.
Some people dislike the use of swap and disable it, but Linux still does some kind of “swap out” when it needs. Linux will swap out file-backed pages (opened files and running executable files) in this case, not using swap space but still needing I/O.
This situation sounds like a Linux swap mechanism. It’s likely that at certain times you’ve encountered low memory issues, causing Linux to swap out so many pages.
To help us understand, what applications do you have installed?
