The Synology offsite backup target (/mnt/synology-backup, surfaced via
the PVE host NFS mount) sits at ~94% by design and was firing
NodeFilesystemFull continuously. Per user request, raise the threshold
to 95% (<5% free). NOTE: NodeFilesystemFull is a global node-filesystem
rule, so this also loosens the warning on k8s node/system disks;
BackupDiskFull (sda /mnt/backup) stays at 85%.
Also adds docs/runbooks/synology-storage.md: how to assess Synology
usage WITHOUT du (Storage Analyzer weekly CSVs, df/btrfs/qgroup),
btrfs async/snapshot-pinned reclaim, the 2026-06-05 capacity assessment
(94% full; Backup share 4.42TiB), and ~500GiB of homelab cleanup
candidates (redundant gphotos Takeout, old laptop VM images, archives).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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