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local-zfs: mention zfs_arc_max clamping by the installer

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This was forgotten to be updated when it changed it the installer and
now reported in the forum [0] that the docs are a bit outdated in this
regard.

[0] https://forum.proxmox.com/threads/hat-proxmox-8-neue-zfs_arc_max-settings.142754/

Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
This commit is contained in:
Christoph Heiss 2024-03-05 13:13:00 +01:00 committed by Thomas Lamprecht
parent c6d5bae84a
commit 2172bbb2be
1 changed files with 12 additions and 7 deletions
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local-zfs.adoc
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@ -570,11 +570,16 @@ Limit ZFS Memory Usage
~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~
ZFS uses '50 %' of the host memory for the **A**daptive **R**eplacement ZFS uses '50 %' of the host memory for the **A**daptive **R**eplacement
**C**ache (ARC) by default. Allocating enough memory for the ARC is crucial for **C**ache (ARC) by default. For new installations starting with {pve} 8.1, the
IO performance, so reduce it with caution. As a general rule of thumb, allocate ARC usage limit will be set to '10 %' of the installed physical memory, clamped
at least +2 GiB Base + 1 GiB/TiB-Storage+. For example, if you have a pool with to a maximum of +16 GiB+. This value is written to `/etc/modprobe.d/zfs.conf`.
+8 TiB+ of available storage space then you should use +10 GiB+ of memory for
the ARC. 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
GiB/TiB-Storage+. For example, if you have a pool with +8 TiB+ of available
storage space then you should use +10 GiB+ of memory for the ARC.
ZFS also enforces a minimum value of +64 MiB+.
You can change the ARC usage limit for the current boot (a reboot resets this You can change the ARC usage limit for the current boot (a reboot resets this
change again) by writing to the +zfs_arc_max+ module parameter directly: change again) by writing to the +zfs_arc_max+ module parameter directly:
@ -583,8 +588,8 @@ change again) by writing to the +zfs_arc_max+ module parameter directly:
echo "$[10 * 1024*1024*1024]" >/sys/module/zfs/parameters/zfs_arc_max echo "$[10 * 1024*1024*1024]" >/sys/module/zfs/parameters/zfs_arc_max
---- ----
To *permanently change* the ARC limits, add the following line to To *permanently change* the ARC limits, add (or change if already present) the
`/etc/modprobe.d/zfs.conf`: following line to `/etc/modprobe.d/zfs.conf`:
-------- --------
options zfs zfs_arc_max=8589934592 options zfs zfs_arc_max=8589934592