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PVE: Raise ZFS ARC max from 6.2 GiB to 16 GiB #3

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opened 2026-05-23 09:18:48 +00:00 by fkrebs · 0 comments
fkrebs commented 2026-05-23 09:18:48 +00:00
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Current state

zfs_arc_max = 6669991936 (~6.2 GiB). Host has 64 GiB RAM with 19 GiB available. ARC hit ratio is excellent (~98.6%) but cache is likely constrained.

Blocker

CT101 (HAOS KVM) is allocated 32 GiB. Right-size CT101 first — then safely raise ARC to 16 GiB without OOM risk.

Steps (after CT101 right-sizing)

  1. Set in /etc/modprobe.d/zfs.conf: options zfs zfs_arc_max=17179869184
  2. echo 17179869184 > /sys/module/zfs/parameters/zfs_arc_max (live, no reboot)
  3. Monitor with cat /proc/spl/kstat/zfs/arcstats | grep size

Risk

Medium — wait for CT101 right-sizing first. Tracked in RESUME.md §Planned.

## Current state `zfs_arc_max = 6669991936` (~6.2 GiB). Host has 64 GiB RAM with 19 GiB available. ARC hit ratio is excellent (~98.6%) but cache is likely constrained. ## Blocker CT101 (HAOS KVM) is allocated 32 GiB. Right-size CT101 first — then safely raise ARC to 16 GiB without OOM risk. ## Steps (after CT101 right-sizing) 1. Set in `/etc/modprobe.d/zfs.conf`: `options zfs zfs_arc_max=17179869184` 2. `echo 17179869184 > /sys/module/zfs/parameters/zfs_arc_max` (live, no reboot) 3. Monitor with `cat /proc/spl/kstat/zfs/arcstats | grep size` ## Risk Medium — wait for CT101 right-sizing first. Tracked in RESUME.md §Planned.
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Reference: fkrebs/docs#3
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