Very noisy RAIDZ2 when playing a video in Plex but not when copying data off the same array

So my TrueNAS box is in the living room temporarily due to moving houses. All my media is on an 8 disk RAIDZ2 (Exos X16 drives). The recordsize is 128k, which I guess I SHOULD have set to 1m before putting all my data on it.

Whenever I play something in Plex, the thing makes quite a bit of noise as if the heads keep having to look for fragmented files. It’s audible above the movie audio and it’s driving me nuts.

So I was doing some testing today and was copying some movie files over to an SSD, so I could write them back onto the old dataset after changing that one to recordsize=1m. I was expecting it to be noisy for 24 hours while reading off the RAIDZ2 but it’s dead quiet while copying the files onto the SSD.

HOW??? Why would it make so much noise when it’s reading one simple 20-40GB MKV file in Plex, but when using cp to copy files to an SSD the whole HDD array is quiet as a mouse.

When I wrote all the files from my old Synology onto this machine I had two rsync jobs running so make use of the Synologys 2x1GE NICs. I was thinking it maybe fragmented the hell out of the files, but AFAIK ZFS being CoW it shouldn’t? The copying onto the SSD kinda proves that I guess, since it’s quiet.

[EDIT] Plex and it’s DB etc is not on this same array. It lives on an NVME pool.

Maybe something to do with transcoding? If you have the full build, I don’t think the Xeon 3204 supports Quicksync. What happens if you play a movie without Plex transcoding it.

It’s not transcoding.

I tried playing a file through Infuse (Plex as backend) and the array makes noise. Whenever I cat that same file to /dev/null it make nearly no noise.

The heck? When running fatrace -t | grep tank I can see it is only reading the MKV, its not writing or reading other files at all.

Im confused now.

This is not the noise when a file is being played but TrueNAS/ZFS is doing this 24/7 to my disks. It’s driving me crazy. There is zero activity on the array either.

Can you tell if it coming from one disk or all the disks? This might be difficult since there are no per-disk activity lights.

What does it show in TrueNAS under Reports if you set it up to show disk activity, for example;

That box does have a lightly used VM, so the disk activity doesn’t stay at 0 for me, but It does go to 0 for periods longer than a few seconds.

What does smartctl say about the health of the disks?

iostat shows zero activity. There are activity lights but they are blocked when a drive is inserted haha.

idk, it’s weird af and driving me crazy.

HI @Fossil, what is the fragmentation % on your ZFS pool?

What happens if you try another large sequential transfer is it still loud?

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Fragmentation is 0%. A couple of days ago I moved about 5TB off my array onto one SSD and it was nearly silent.

Aside from the noise when playing videos, also the rythmic sounds it makes when doing nothing makes me worry about the longevity of my drives. It’s doing “something” 24/7.

While not 100% similar, this is a bit interesting as it’s ZFS and Plex. I say that because the age of this post it has to be TrueNAS Core (FreeBSD based of course). But it’s interesting that this user had small amounts of I/O constantly while Plex was running (even if idle and not streaming).

You mentioned when you try playing a file through Plex, but what happens if you stop Plex altogether?

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I actually spoke to a Seagate engineer and he asked the firmware team. Background operations on these disks cannot be stopped by any firmware settings.

What I did do was re-enable head parking after 2 mins. So now at least it’s quiet after 120s of doing nothing since background operations don’t run in IDLE_B mode (heads parked).

Still noisy as hell when playing video through Plex. Probably because it’s HTTP based and bursty, while playing it over SMB means it just streams and buffers continuously.