TrueNAS Scale - intense CPU activity after SMB file copy

TrueNAS General
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I set up a TrueNAS Scale test server to gain familiarity, prior to upgrading from Core to Scale on a main unit. The server was built with repurposed hardware thus:

  • OS: TrueNAS Scale 24.10.1
  • M/B: MSI B75IA-E33 mini-ITX
  • CPU: Intel i5 3570K (4C/4T)
  • RAM: 16MB non-ECC
  • 4 x Kingston 256BG SSD in RAIDZ1
  • Boot: 128GB NVMe internal USB3 adapter
  • Case: Silverstone Milo ML05

I am well aware that there are some compromises with this build. For instance the file copying process bitrate from Windows to the test server is highly variable and never more than 40 KB/sec, which I put down to the less-than-capable RealTek NIC on the B75 motherboard. Also there is differential cooling between the processor cores that I need to sort out.

Anyway, there is an SMB fileshare set up on this test server and Plex app installed. I was testing the ability to copy across video files (MPEG2 as MKV or AVC as TS containers) via SMB, to check the ability of Plex to recognise the new files in its designated folders and fetch the metadata.

With each copy I noticed a burst of CPU activity - signalled by the CPU fan accelerating up - which occurs after the individual files are copied across, and takes the CPU temperature up to 60C and then 80C for a few minutes. There is an annotated figure of the CPU activity graphs below, showing the post-copy CPU intense activity (orange line and filled area) after copying 3 video files:

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Does anyone know what this activity could be? It’s not shown in the figure but the length of increased CPU activity seems related to the size of the video file. Therefore I thought about ZFS trying to compress the already-compressed video files, but my understanding from reading older forum posts is that ZFS may try this, but give up when it figures out the files are already compressed; plus that it would be relatively low-impact process. On the other hand, this advice was before TrueNAS Scale was out. Alternatively, I can’t believe that this is the Plex metadata acquisition; the CPU is a bit old now but surely that shouldn’t be such an intensive process.

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Plex doing Plex things after it sees the files? Have you looked at TOP in CLI?

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Thanks for the reply! No I haven’t as I didn’t know what that is… :grinning:
Also for CLI I have yet to set up SSH into the box.

I’ve found some references for TOP in Linux and will read them for starters.

Thanks again!

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Update: OK looks like Plex-related processes, as you suggested:

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image1297×841 145 KB

I thought the Plex transcoding only occurred when playing back / streaming the video, not after simply copying the files in. Anyway I see from the Plex help documentation that this process is always set to ‘very fast’ by default, but can be changed in the Plex Mediaserver app.

Highest CPU load is the Plex Media Scan process? Better see if I can also change some parameters.

Strange thing is that a separate Plex install on the main server (TN Core 13.3) doesn’t exhibit this after file copy.

Many thanks again for the pointer to using TOP.

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