Matt
fd211aae51
The cold ZFS pool is a backup tier only — hot data (MC world, Gitea,
Directus DB, containers) lives on NVMe LVM, not ZFS. So ARC's default of
50% RAM was wasted: nothing it could cache was hot enough to matter, and
the ~16GB cache crowded MC out of RAM, pushing 2.4GB into swap.
This file lives in the repo for reproducibility; it gets dropped into
/etc/modprobe.d/ on the host and applied immediately via
/sys/module/zfs/parameters/zfs_arc_{max,min}.
Effect on glados:
before: used=27/31GB, free=748MB, ARC=15.6GB
after: used=~10GB, free=~14GB, ARC=1.0GB (1-2GB range)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
18 lines
845 B
Plaintext
18 lines
845 B
Plaintext
# ZFS ARC sizing for glados — a mixed-workload host (32 GB RAM).
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#
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# Why these numbers:
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# - The cold ZFS pool is BACKUP TIER ONLY. Hot data (MC world, Gitea repos,
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# Directus DB, containers) all live on NVMe LVM, not ZFS — so a large
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# ARC doesn't help any of the actual workloads.
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# - Tier-2 backup work is streaming writes (rsync hot→cold every 4h):
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# streaming writes don't benefit much from cache.
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# - Reads happen rarely (disaster recovery, Gitea LFS fetches), and a
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# one-time cold read is fine.
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# - MC is the memory-hungry workload (10 GB Java heap). Every GB we DON'T
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# give to ARC is a GB more headroom for MC and future content.
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#
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# 2 GB max / 1 GB min keeps ZFS metadata + small ARC for occasional reads,
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# without crowding MC out of RAM.
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options zfs zfs_arc_max=2147483648
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options zfs zfs_arc_min=1073741824
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