zfs_arc_max default value

[ieronymous]

I was searching a completely different issue while I edited the /etc/modprobe.d/zfs.conf file where I noticed that
options zfs zfs_arc_max=13476298752

My system has 128Gb or ram and though that by default zfs_arc_max tries to almost limit that ram amount (at least in older PVe versions).
Instead here it is set by default to use 13476298752 which in case that this number is in bytes, equals to only 12.55 Gigabytes.

 

[billy999]

For new installations starting with Proxmox VE 8.1, the ARC usage limit will be set to 10 % of the installed physical memory, clamped to a maximum of 16 GiB

Looks correct to me.

 

[ieronymous]

Looks correct to me.

Thank you for your quick response.

Won't this amount of limitation though, makes the use of ssds mandatory again?

 

[billy999]

Thank you for your quick response.

Won't this amount of limitation though, makes the use of ssds mandatory again?

If you want to use more memory for ARC, you have to set it explicitly. https://pve.proxmox.com/wiki/ZFS_on_Linux

 

[ieronymous]

If you want to use more memory for ARC, you have to set it explicitly. https://pve.proxmox.com/wiki/ZFS_on_Linux

yes, I know how and the recommendations were (at time of reading) no below 4Gbs no more than 64Gbs.
Upon that recommendation, 13Gb seemed a bit on the low side.

 

[billy999]

yes, I know how and the recommendations were (at time of reading) no below 4Gbs no more than 64Gbs.
Upon that recommendation, 13Gb seemed a bit on the low side.

Defaults arent recommendations. The recommended max value is as much as possible without OOMing, which depends on your setup. The recommended min value is 2 GiB Base + 1 GiB for each TiB-Storage