EDIT: This ended up being a scrub process. Run zpool status -v and read the scan status for your pool clearly.

I have a TrueNAS server running FreeBSD and this morning at 12 AM the disks started to be read from constantly. I thought this was some snapshot task, so I disabled my snapshots and restarted the server, but every time I restart the server it continues to read from my storage pool. I have stopped all running jails as well and the disks still show IO (the screenshots below are with jails running, but they look the same with jails stopped).

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I can't figure out which process is causing this. I tried using top -m io, but this shows no R/W activity.

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According to this resource, top -m io doesn't work on FreeBSD so I can't find out which process is reading from my disks:

top io mode doesn't properly display stats

I have tried checking if there are any running snapshot tasks using ps -aux | grep rsync, but nothing shows except my grep command.

Here's some resources I've checked:

Is it possible to get the top command working? I just want to know what process is reading from my disks and kill it.

  • Have you try with htop? Commented Aug 27, 2023 at 9:46
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    htop does not show RBYTES on FreeBSD, but this ended up being a scrub process. Thanks anyway! Commented Aug 27, 2023 at 9:58

1 Answer 1



top -a -m io

…should do the trick! If there’s no process associated with a heavy I/O - it’s kernel and you can’t really do anything about it. I mean no way to query.

It could be ZFS performs some integrity checks / scrubbing, so it might be a good lead. Take a look here:


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    I feel so dumb now. It is the scrub process. I ran "zpool status -v" and see that for my storage pool "scrub in progress since Sun Aug 27 00:00:02 8.06T scanned...", so just have to let it finish. facepalm Commented Aug 27, 2023 at 9:57
  • 1
    Dude you’re OK! Take it easy and just let it go. Seriously! :) Commented Aug 28, 2023 at 19:44

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