Small ARC?

[cwagz]

Se

On 22.02.3 it looks like I am stuck with an ARC of 3.6GiB even when setting zfs_arc_max to 0.

Any ideas or suggestions?

Setting the this to an actual number (1/2 of RAM or more) works. I just no longer see the ARC grow if I set to 0 after updating to 22.02.3.

 

[cwagz]

I just noticed that whatever I set zfs_arc_max to gets overwritten at some point by the system without a reboot.

So, as it stands right now, my 128GiB system gets an arc setting of 32GiB assigned. This is a big improvement over the 3.6GiB that was being set when I had 64GiB of RAM but still way less that what I think it should be. I have 44GiB RAM allocated to my virtual machines. I am also running one instance of the PLEX app.

 

[fa2k]

@cwags , here's a suggestion, but it ain't pretty. I've used a Init/Shutdown script under System Settings, Advanced.

echo SIZE_IN_BYTES >> /sys/module/zfs/parameters/zfs_arc_max

(I've edited the post a bit, because I missed part of the thread when reading it)

 

[cwagz]

@cwags , here's a suggestion, but it ain't pretty. I've used a Init/Shutdown script under System Settings, Advanced.

View attachment 57782

(I've edited the post a bit, because I missed part of the thread when reading it)

Thank you. I actually had tried this, but it seems like the system is actually overwriting the value at some point while running. It had reverted on me without a reboot. Maybe starting / stopping a VM triggers the value to be overwritten by the system?

 

[fa2k]

Ok, you're way ahead of me.

Now that you say it - I see the same thing! I configured mine to be 110 GB on boot. With one 12 GB VM and one 1 GB VM, mine reads 97 GB now (104152956928). Makes perfect sense. (I can't work out how you get 32 GB ARC from 128 GB RAM and 44 GB VMs though - maybe only 20 GB active VMs, and it start at half RAM?).

I had already accounted for the VMs in my setting of 110GB, so I'll bump that a bit, good to know this.

 

[fa2k]

I had already accounted for the VMs in my setting of 110GB, so I'll bump that a bit, good to know this.

Check this reply on the other thread https://www.truenas.com/community/t...default-tuning-zfs_arc_max.101463/post-712452

It may be dangerous to go too close to max - ARC could use a lot more RAM due to fragmentation

 

[cwagz]

@fa2k - Thanks for the heads-up. I am just letting it manage itself. It’s weird how small it is. I am at 18.9GB arc right now. I am not sure why it keeps deciding on a different size.