Hi, thanks for looking into this!
On 26/02/2026 09:47, Maximiliano Sandoval wrote:
> We rephrase the current section putting more emphasis on the current
> state of things given than Proxmox VE 8.1 was released over two years
> ago.
>
> We also document ZFS' default size. See [zfs-6a629f3] for more details.
>
> This also frames the problem for pre-existing setups in its own
> paragraph.
>
> [zfs-6a629f3]
> https://github.com/openzfs/zfs/commit/6a629f32344468ae81b264055916641480cb438d
>
> Signed-off-by: Maximiliano Sandoval <[email protected]>
> ---
> local-zfs.adoc | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/local-zfs.adoc b/local-zfs.adoc
> index 85fa092..b3a462d 100644
> --- a/local-zfs.adoc
> +++ b/local-zfs.adoc
> @@ -586,10 +586,15 @@ configured for the root user.
> Limit ZFS Memory Usage
> ~~~~~~~~~~~~~~~~~~~~~~
>
> -ZFS uses '50 %' of the host memory for the **A**daptive **R**eplacement
> -**C**ache (ARC) by default. For new installations starting with {pve} 8.1,
> the
> -ARC usage limit will be set to '10 %' of the installed physical memory,
> clamped
> -to a maximum of +16 GiB+. This value is written to
> `/etc/modprobe.d/zfs.conf`.
> +ZFS uses '10 %' of the host memory, clamped to a maximum of +16 GiB+, for the
> +**A**daptive **R**eplacement **C**ache (ARC) by default. This value is
> written
> +to `/etc/modprobe.d/zfs.conf` during installation.
> +
> +Before {pve} 8.1, the ARC usage limit was not set during installation and
> +matched ZFS' default value which was either 62.5% starting on ZFS 2.3.0 or
> 50%
I'm not sure there is a case where a user could have PVE < 8.1 but ZFS
>= 2.3? But it's probably OK to still mention the 62.5%.
There is one more complication: IIRC PVE 8.1 installers only set the ARC
size limit when installing on ZFS, so e.g. installations on ext4+LVM
which later got a zpool would still have ZFS defaults. This was only
changed with the PVE 8.4 installer I think [1], now all installations
limit the ARC size.
> +for older versions. For existing installations that predate {pve} 8.1, manual
> +steps would have to be performed in order to lower the usage limit as
> described
> +below.
>
> Allocating enough memory for the ARC is crucial for IO performance, so
> reduce it
> with caution. As a general rule of thumb, allocate at least +2 GiB Base + 1
[1] https://bugzilla.proxmox.com/show_bug.cgi?id=6285
