Initial commit: Hermes Agent Skills collection
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# ZFS-to-Ceph Migration Analysis (2026-07-03)
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## Context
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User wants to decommission osd.1 (USB-connected Hitachi HDD on proxmox1, slow BlueStore ops)
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and replace it with disks from the ZFS pool on 10.0.30.100. Initial assumption was "9×2.7TB"
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but actual inventory revealed 4×3TB in RAIDZ2 + 2 free disks + 2 already in Ceph.
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## Disk Inventory (10.0.30.100, 2026-07-03)
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| Disk | Model | Serial | Size | POH | Age | SMART | Role | Verdict |
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|------|-------|--------|------|-----|-----|-------|------|---------|
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| sda | Crucial MX300 SSD | 164914EEB886 | 275GB | 81,871 | 9.3y | ✅ 0/0/0 | Boot SSD (swap→DB for osd.8) | Keep — sda3 now DB device |
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| sdb | WD30EFRX Red+ | WCC4N4VRJ5UU | 3TB | 81,786 | 9.3y | ✅ 0/0/0, CRC=3 | ZFS pool | Oldest in pool, first offline candidate |
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| sdc | WD30EZRX Green | WMC1T2256499 | 3TB | 89,262 | 10.2y | ⛔ 371 pending, 243 uncorr | Free | REJECT — defective |
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| sdd | WD30EFRX Red+ | WCC4N4SVR8JL | 3TB | 57,925 | 6.6y | ⚠️ 16 pending, 15 uncorr, Self-test FAIL | Free | REJECT — confirmed read failure |
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| sde | WD30EFRX Red+ | WMC4N2399595 | 3TB | 104,327 | 11.9y | ✅ 0/0/0 | Ceph osd.8 | Active, very old. NOW HAS DB ON SSD |
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| sdf | WD30EFRX Red+ | WMC4N2400243 | 3TB | 98,475 | 11.2y | ✅ 0/0/0 | Ceph osd.9 | Active, very old. NO DB device |
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| sdg | WD30EFZX Purple | WX12DA01FUA7 | 3TB | 30,901 | 3.5y | ✅ 0/0/0 | ZFS pool | Best candidate |
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| sdh | WD30EFZX Purple | WX12DA0R1NFH | 3TB | 30,901 | 3.5y | ✅ 0/0/0 | ZFS pool | Best candidate |
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| sdi | WD30EFZX Purple | WX22DA0D7EP3 | 3TB | 30,900 | 3.5y | ✅ 0/0/0 | ZFS pool | Best candidate |
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## SMART Self-Test History (sdd)
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```
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Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error
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# 1 Short offline Completed: read failure 90% 57925 62939576
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# 2 Short offline Completed without error 00% 50673 -
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# 3 Extended offline Completed: read failure 10% 50659 63009384
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# 4 Short offline Completed without error 00% 50651 -
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```
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Two read failures at LBA ~63M (~32GB region), 7000h apart. Progressive degradation.
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## badblocks Test (sdd)
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- Command: `badblocks -wsv -b 4096 /dev/sdd`
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- Started: 2026-07-03 12:25:31 CEST
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- Killed by user request at ~3.4% (Pattern 1/4: 0xaa)
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- Errors found: 0 (but test was aborted early)
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- Log: `/tmp/badblocks_sdd.log` on 10.0.30.100
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- Verdict: Inconclusive (early abort), but SMART self-test failure already disqualifies disk
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## ZFS Pool Details
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```
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Pool: pool01_n2_redundant
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Type: RAIDZ2 (2 parity)
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Disks: sdg, sdh, sdi, sdb (4× 2.73TB)
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Raw: 10.9TB
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Usable: ~5.46TB (2 data + 2 parity)
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Used: 3.63TB (66%)
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Free: 1.87TB
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Fragmentation: 57%
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Health: ONLINE, 0 errors
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Dedup: 1.12x
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Scrub: Monthly, last 2026-06-28, 0 errors
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```
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Datasets: Docker volumes, TimeMachine (~951GB), proxmox_nfs (~963GB), HomeAssistant.
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## Ceph State (2026-07-03)
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- Health: HEALTH_WARN (BLUESTORE_SLOW_OP_ALERT on osd.0 & osd.1)
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- 10 OSDs up/in, 12TB raw, 5.1TB used, 7.0TB free
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- osd.1: USB Hitachi HDD 3.6TiB on proxmox1 (10.0.20.10), slow ops
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- 7 pools active
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## Migration Strategies Evaluated
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### Option A: One-shot migration (recommended)
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1. Migrate all 3.63TB ZFS data → Ceph (has 7.0TB free)
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2. `zpool destroy` → all 4 disks freed
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3. Create 4 new Ceph OSDs on n5pro
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4. Purge osd.1
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### Option B: Phased with ZFS degradation (CHOSEN)
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1. `zpool offline pool sdb` (oldest disk) → wipe → Ceph OSD (+3TB)
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2. ZFS now degraded (1 parity left), migrate data to Ceph
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3. `zpool destroy` → wipe sdg/sdh/sdi → 3 more Ceph OSDs (+9TB)
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**Chosen**: Option B — allows incremental Ceph growth while ZFS data is migrated gradually.
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### Rejected: 2-disk offline
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Offlining 2 disks from RAIDZ2 leaves 0 redundancy. Too risky during active data migration.
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## OSD DB/WAL Acceleration Analysis (2026-07-03)
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### Which OSDs Have/Lack DB Devices
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| OSD | Host | HDD | DB on Flash? | Flash Available | Free on Flash |
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|-----|------|-----|-------------|-----------------|---------------|
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| osd.1 | proxmox1 | sdc 3.6TB | ❌ | ✅ 1TB Toshiba NVMe | 848 GB — BUT osd.1 being decommissioned |
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| osd.7 | proxmox7 | sda 982GB | ✅ 50GB ceph-db | ✅ 256GB Toshiba NVMe | 110 GB |
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| osd.8 | ubuntu(.30.100) | sde 2.7TB | ✅ NOW 30GB on sda3 | 256GB Crucial SSD | 0 (swap consumed) |
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| osd.9 | ubuntu(.30.100) | sdf 2.7TB | ❌ | Same SSD, no space | ❌ Needs root shrink or new SSD |
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| osd.10 | proxmox6 | sda 982GB | ✅ 50GB ceph-db | ✅ 256GB Toshiba NVMe | 110 GB |
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### DB Device Addition: osd.8 (2026-07-03, SUCCESSFUL)
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**Method**: Repurposed 32GB swap partition (sda3) on boot SSD as LVM-backed DB device.
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Steps taken:
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1. `swapoff /dev/sda3` (1.5GB used, 6.4GB RAM free — safe)
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2. `wipefs -a /dev/sda3`
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3. `pvcreate /dev/sda3` → `vgcreate ceph-db-vg /dev/sda3` → `lvcreate -L 30G -n osd-8-db ceph-db-vg`
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4. `systemctl stop ceph-osd@8`
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5. `ceph-volume lvm new-db --osd-id 8 --osd-fsid <fsid> --target ceph-db-vg/osd-8-db`
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6. `systemctl start ceph-osd@8`
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Result: osd.8 up with `block.db → /dev/dm-2`, `devices = sda,sde`. BlueFS spillover warning (1.1GB on HDD, 231MB on SSD) — expected to clear as compaction migrates data.
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### Key Lesson: ceph-bluestore-tool vs ceph-volume
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`ceph-bluestore-tool --command bluefs-bdev-new-db` FAILS on Ceph Squid 19.2.x with `"No valid bdev label found"` — tried raw partition, LVM LV, with/without zap, as root and ceph user. The working tool is `ceph-volume lvm new-db` (requires LVM-formatted target, not raw partition).
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## Key Lessons
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1. **RAIDZ cannot shrink** — `zpool remove` doesn't work on RAIDZ vdevs. Only `zpool offline` (temporary) or `zpool destroy` (permanent) can free disks.
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2. **SMART PASSED ≠ healthy** — sdd passed overall SMART assessment but had confirmed self-test read failures. Always check self-test log, not just overall health.
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3. **Assumptions about disk counts are dangerous** — "9×2.7TB" was wrong; actual was 4×3TB in ZFS + 2 free + 2 in Ceph. Always verify with `lsblk` + `zpool status` before planning.
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4. **badblocks -wsv is destructive and slow** — 4 patterns × ~5h per 3TB = ~20h total. Only run on disks committed to repurposing. Can be killed early if SMART already disqualifies.
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5. **SSH key selection** — 10.0.30.100 accepts `~/.ssh/id_ed25519_proxmox` (root), NOT the Galera key from 1Password.
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6. **ceph-bluestore-tool bluefs-bdev-new-db is broken on Squid** — Use `ceph-volume lvm new-db` instead. Requires LVM LV as target, not raw partition.
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7. **BlueFS spillover after adding DB is normal** — Existing RocksDB SSTs stay on HDD, new writes go to flash. Warning clears as compaction progresses.
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8. **Swap can be safely repurposed for DB** — If RAM is adequate (>4GB free with swap nearly empty), disabling swap to reclaim flash for Ceph DB is viable. Consider zram as swap replacement.
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9. **ZFS has no defrag command** — Fragmentation (e.g. 57%) only affects freespace map efficiency, not file integrity. The ONLY way to "defrag" ZFS is: copy data elsewhere -> destroy pool -> recreate -> copy back. Irrelevant if migrating off ZFS entirely.
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10. **RAIDZ disk removal is permanent degradation** — Pulling 1 disk from RAIDZ2 drops to RAIDZ1-equivalent (1 parity). ZFS marks the disk UNAVAIL but it stays in the vdev config. `zpool detach` does NOT work on RAIDZ members. Pool continues degraded until destroyed.
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11. **zfs destroy -r enters D-state on degraded pools** — On RAIDZ2 with defective disks, `zfs destroy -r` can hang in uninterruptible I/O (D-state) for 10+ minutes. Cannot be killed. Plan accordingly -- run in background.
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12. **ZFS async free lag** — After `rm -rf` on ZFS, `zfs list` shows OLD usage for minutes/hours. `du -sh` shows actual live data. The gap is TXG-async free, resolves automatically. Don't panic if `zfs list` says 290GB but `du` says 3GB.
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13. **Background monitor processes block zfs destroy** — Processes with `cwd` inside the dataset (including your own polling loops) prevent `zfs destroy`. Use `lsof +D <path>` and `fuser -mv <path>` to find ALL blockers, kill them first.
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14. **n5pro WAL/DB prep pattern** — Remove unused `pve/data` thin pool (0% allocated, not in storage.cfg) via `lvremove pve/data`, then `lvcreate -L 30G -n wal-db-osd-X pve` for each new OSD. Verified on n5pro (10.0.20.91, 128GB NVMe, gained 70GB for 2x 30GB DB LVs).
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