[solved] How to limit max arc size on TrueNAS SCALE?

[thomasesrichter]

I found an option on the misc menu, but that seems to relate to the way FreeBSD used to do it, I think ZFs on Linus is a different method, since Every reboot the system files reset I don't know where I can configure an ARC size limit. A little documentation for the BETA at least would be nice.

 

[morganL]

We're using OpenZFS 2.0 within SCALE. Documentation on the parameters are here:

zfs-module-parameters.5 — OpenZFS documentation

openzfs.github.io

 

[thomasesrichter]

We're using OpenZFS 2.0 within SCALE. Documentation on the parameters are here:

zfs-module-parameters.5 — OpenZFS documentation

openzfs.github.io

I wanted to know if there is a place in the TrueNAS SCALE webgui where I can set these settings.

 

[morganL]

System tunables would be my assumption, but I haven't tried it myself. Anyone else experimented with this?

Tunables |

Tunables

www.truenas.com

 

[thomasesrichter]

System tunables would be my assumption, but I haven't tried it myself. Anyone else experimented with this?

Tunables |

Tunables

www.truenas.com

That's what I'm saying, there is no System Tunables in SCALE yet. there is only this misc option under System Settings that gives me this "Platform-Dependent" option of Sysctrl that looks like the system tunables, but being platform dependent I don't think its meant for the Debian distribution that comes on the TrueNAS SCALE ISO.

Screenshots:

 

[thomasesrichter]

We're using OpenZFS 2.0 within SCALE. Documentation on the parameters are here:

zfs-module-parameters.5 — OpenZFS documentation

openzfs.github.io

I Think this is more suited for my predicament, I might try to set these manually and see if it persists on reboot, since most changes made outside the WebGUI on SCALE seems to reset on system reboot. (Which kinda behaves like a Fedora Silverblue, immutable system).

 

[thomasesrichter]

forgot to add a link:

Module Parameters — OpenZFS documentation

openzfs.github.io

 

[thomasesrichter]

No dice, I tried
echo 3221225472 >> /sys/module/zfs/parameters/zfs_arc_max
and rebooted the system but after restart it return 0 (half the system memory)

 

[morganL]

A boot script could set the arc size at each boot time.

 

[thomasesrichter]

A boot script could set the arc size at each boot time.

I thought about that, but I don't really know if this property is effective at runtime or if it needs as reboot to work like sysctl. Can anyone confirm?

 

[morganL]

It should be runtime.... => could be run after boot.

 

[thomasesrichter]

Can confirm, the way to limit max arc size on TrueNAS SCALE is to create a preinit command on the "Init/Shutdown Scripts" page under "Data Protection" menu with the command:

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

where SIZE_IN_BYTES should be replaced by, would you know, the size you want in bytes, such as 2147483648 for 2GB

 

[burmjohn]

Can confirm, the way to limit max arc size on TrueNAS SCALE is to create a preinit command on the "Init/Shutdown Scripts" page under "Data Protection" menu with the command:

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

where SIZE_IN_BYTES should be replaced by, would you know, the size you want in bytes, such as 2147483648 for 2GB

Just to add to this, in case you wanted to test these changes w/o a reboot, you can issue that same command in shell for it take effect right away. But obviously don't forget to do the above for persistence across reboots.

 

[dirtyfreebooter]

Can confirm, the way to limit max arc size on TrueNAS SCALE is to create a preinit command on the "Init/Shutdown Scripts" page under "Data Protection" menu with the command:

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

where SIZE_IN_BYTES should be replaced by, would you know, the size you want in bytes, such as 2147483648 for 2GB

while this was working running this command in init/shutdown scripts, randomly after 10+ days of uptime, it seems to reset itself..

my init script (i have 256 GiB of ram)

Code:

echo 240518168576 > /sys/module/zfs/parameters/zfs_arc_max

seeing only half in use on dashboard, checking zfs parameter

Code:

# cat /sys/module/zfs/parameters/zfs_arc_max
134925107200

somehow this reset itself. IMHO, TrueNAS SCALE needs some separate section in the advanced settings specifically for ZFS, given this is a ZFS NAS.

 

[morganL]

Please add a suggestion via TrueNAS "report-a-bug".... we try to prioritise these activities based on user demand and upvotes.

 

[dirtyfreebooter]

Please add a suggestion via TrueNAS "report-a-bug".... we try to prioritise these activities based on user demand and upvotes.

https://jira.ixsystems.com/browse/NAS-114217

 

[appliance]

is Sysctl working at all? I have the items "Generated by autotune" and only now i realized none of them apply, nor can be found with sysctl. In that case, it's not a suggestion but an issue(?)

 

[dirtyfreebooter]

no sysctl is not really a thing anymore in linux. that is a CORE/Freebsd thing. see posts above

 

[rotelly]

I have noticed that when scale starts/stops VMs it will adjust the value in

## Before Boot of VM with 8 GB of memory
root@blackhole[~]# echo 51539607552 > /sys/module/zfs/parameters/zfs_arc_max
root@blackhole[~]# cat /sys/module/zfs/parameters/zfs_arc_max
51539607552

## After VM Boot
root@blackhole[~]# cat /sys/module/zfs/parameters/zfs_arc_max
42000932864

 

[inman.turbo]

instead of scaling back ARC when a vm started which needs some of that memory, scale will just warn you, then crash your system (out of memory)