Initial planning docs and hardening scripts for HA rebuild

Covers node 1 hardware/network layout, LVM-thin -> ZFS migration path, Ceph as the future HA storage upgrade, and baseline SSH/firewall hardening.
2026-07-20 11:45:54 +10:00
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+# Storage: LVM-thin → ZFS, and the path to Ceph
+
+## Why move off LVM-thin
+
+Neither ZFS nor LVM-thin is shared storage — both are node-local. HA needs
+a VM's disk reachable from more than one node so it can restart elsewhere
+on host failure. LVM-thin has no answer for that. ZFS does, via
+replication; Ceph does natively.
+
+## Two paths to HA-capable storage
+
+| | ZFS + replication | Ceph |
+|---|---|---|
+| Nodes required | 1+ (replication needs 2+ targets) | 3+ |
+| Consistency | Async — snapshot-based, as often as every minute | Sync — real shared storage |
+| Data loss on failover | Whatever changed since last replication cycle | ~None |
+| Network needs | Normal cluster link | Fast dedicated network (see `03-networking.md`) |
+| Overhead | Low | Higher RAM/CPU/disk |
+
+Starting point: **ZFS + replication**. Revisit Ceph once 3 nodes exist or
+zero-RPO failover is worth the overhead.
+
+## Migration plan (old hardware → new hardware)
+
+Don't convert the old LVM-thin box in place. Rebuild fresh on new
+hardware with ZFS from the installer (mirror if 2+ disks), then move VMs:
+
+1. On the old host: `vzdump` each VM to a backup file (external drive,
+   NFS share, or PBS if available).
+2. Copy backups to the new host.
+3. `qmrestore` onto the new ZFS storage — disks land as ZVOLs.
+
+Alternative if both hosts can see each other on the network: temporarily
+cluster them and use the GUI "Migrate" with a storage move (offline only
+— live migration doesn't cross storage types).
+
+## Later: handing Ceph-earmarked disks over
+
+Once nodes 2 and 3 are up and the Ceph-earmarked disks (see
+`01-hardware-node1.md`) can be pooled 3-node minimum:
+
+1. Wipe any temporary ZFS pool on those disks.
+2. Initialize Ceph across the 3 nodes.
+3. Create OSDs directly on the raw disks (no ZFS/RAID underneath).
+4. Migrate VMs that need zero-RPO failover from the ZFS-replicated tier
+   onto Ceph-backed storage.