[PATCH docs 1/2] local-zfs: Rephrase ARC limit

[Maximiliano Sandoval <m.sandoval@proxmox.com>]

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.

This also frames the problem for pre-existing setups in its own
paragraph.

Signed-off-by: Maximiliano Sandoval <m.sandoval@proxmox.com>
---
 local-zfs.adoc | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/local-zfs.adoc b/local-zfs.adoc
index 4f20d00..12506d1 100644
--- a/local-zfs.adoc
+++ b/local-zfs.adoc
@@ -586,10 +586,13 @@ 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 set to '50 %' without clamping it to a
+maximum size. 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
-- 
2.47.3