[SOLVED] zfs_arc_max / /etc/modprobe.d/zfs.conf seems to be ignored in Proxmox 6.0


Well-Known Member
Jan 27, 2018
> cat /sys/module/zfs/version

> cat /etc/modprobe.d/zfs.conf
options zfs zfs_arc_max=8589934592

> update-initramfs -u

> reboot

> cat /sys/module/zfs/parameters/zfs_arc_max

> awk '/^c/ { print $1 " " $3 / 1048576 }' < /proc/spl/kstat/zfs/arcstats
c 32138
c_min 2008.62
c_max 32138
compressed_size 61.1318

Not sure what I'm doing wrong. I tried the reboot and update-initramfs -u two times...
And as far as I can recall I did exaclty the same with Proxmox 5 and there it always worked so maybe it is a 6.0 problem?

Anyways, any help would be appreciated!
This works on my machine. What was the output of the update-initramfs -u?
This works on my machine. What was the output of the update-initramfs -u?

When I rerun it the output is
update-initramfs: Generating /boot/initrd.img-5.0.15-1-pve

Without anything else and I'm quite sure it was the same when I ran it the first time.

Meanwhile I tried to set the size on the fly with
> echo "8589934592" > /sys/module/zfs/parameters/zfs_arc_max
> echo 3 > /proc/sys/vm/drop_caches

This had the somewhat strange effect that `cat /sys/module/zfs/parameters/zfs_arc_max` actually had the correct size but
`awk '/^c/ { print $1 " " $3 / 1048576 }' < /proc/spl/kstat/zfs/arcstats` the stats from above. Now (and after the machine joined a cluster) the stats are as expected:
> awk '/^c/ { print $1 " " $3 / 1048576 }' < /proc/spl/kstat/zfs/arcstats
c 8192
c_min 2008.62
c_max 8192
compressed_size 7119.07

When I look at the "Memory usage" graph of the machine it looks like the memory usage dropped down to the expected amount at the moment the machine joined the cluster but I cannot say for sure. For the moment this is resolved for me since one way or another the machine will respect the max size. Worst case is I have to set it on the fly after a reboot and wait some time. I'm not sure if it's worth to investigate this further though it is a bit odd.
there is a hint a little bit higher up on the same page that links to the boot loader section ;)
I followed this steps to edit the max zfs ram and after that i restarted the machine.
Now my system / gui does not boot.

Commands used:
nano /etc/modprobe.d/zfs.conf
options zfs zfs_arc_max=8589934592

update-initramfs -u

#Proxmox Latest version
#OVH dedicated server
Last edited:
Managed to solve by adding the "5.4.44-1-pve" version to the command...

Commands used:
nano /etc/modprobe.d/zfs.conf

#Max Ram Used by ZFS
options zfs zfs_arc_max=8589934592
#Min Ram Used by ZFS
options zfs zfs_arc_min=1073741824

update-initramfs -k 5.4.44-1-pve -u



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