291 lines
11 KiB
Markdown
291 lines
11 KiB
Markdown
# Ceph RBD Pool Migration (Between Pools with Different Redundancy)
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## When to Use
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Moving CT/VM disk volumes from one Ceph RBD pool to another — typically
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to upgrade redundancy (e.g. size=2 replica pool → EC4+1 erasure-coded pool).
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## Assessing Pool Redundancy
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Before migrating, check the redundancy profile of all pools:
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```bash
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# Per-pool: replication factor and minimum
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for pool in tm_disks vm_disks hdd_disk media_meta media_ec; do
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size=$(ceph osd pool get $pool size 2>/dev/null | awk '{print $2}')
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min=$(ceph osd pool get $pool min_size 2>/dev/null | awk '{print $2}')
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echo "$pool: size=$size min_size=$min"
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done
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# EC profile details
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ceph osd erasure-code-profile get ec41-hdd
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# k=4 m=1 → EC4+1, tolerates 1 failure, 5 OSDs needed
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# Crush rule (which device class, failure domain)
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ceph osd crush rule dump <rule_name>
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```
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### Redundancy Comparison Table (This Cluster)
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| Pool | size | min_size | Tolerates Failure | Type |
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|------|------|----------|--------------------|------|
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| tm_disks | 2 | 2 | **NONE** (read-only on 1 loss) | Replicated HDD |
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| vm_disks | 3 | 2 | 1 OSD/host | Replicated |
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| hdd_disk | 3 | 2 | 1 OSD/host | Replicated |
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| media_meta | 3 | 2 | 1 OSD/host | Replicated (metadata for EC) |
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| media_ec | 5 (EC4+1) | 4 | 1 OSD | Erasure Coded |
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**Warning**: `size=2, min_size=2` means ZERO fault tolerance — losing one
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replica makes the pool read-only. This is a dangerous configuration.
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## Migration Procedure
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### Prerequisites
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- Identify source pool and target pool
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- Target pool must support `content rootdir` (check `/etc/pve/storage.cfg`)
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- For EC pools: metadata pool (e.g. `media_meta`) stores the RBD header,
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data pool (e.g. `media_ec`) stores the chunks. PVE storage config links
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them via `data-pool` directive.
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### Step 1: Remove CT from HA
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```bash
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# On any PVE node (ha-manager is cluster-wide)
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ha-manager remove ct:NNN
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```
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Cannot stop a HA-managed CT directly — HA will restart it. Must remove
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from HA first.
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### Step 2: Stop the CT
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```bash
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# On the node hosting the CT
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pct stop NNN
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# If locked:
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pct unlock NNN # Clear stale locks
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pct delsnapshot NNN <snapname> # Remove snapshots causing locks
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pct shutdown NNN --timeout 10 --forceStop 1 # Force if needed
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```
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### Step 3: Allocate New Volume on Target Pool
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```bash
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# Allocate on target storage (PVE-managed, proper volid format)
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pvesm alloc <target_storage> <vmid> <volume_name> <size>
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# Example: pvesm alloc media 114 vm-114-disk-new 500G
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```
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### Step 4: Copy Data Between RBD Devices
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```bash
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# Map both source and destination RBD images
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SRC_DEV=$(rbd map <src_pool>/<src_volume>)
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DST_DEV=$(rbd map <dst_pool>/<dst_volume>)
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# Block-level copy with dd
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dd if=$SRC_DEV of=$DST_DEV bs=4M status=progress &
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# 500G at ~160 MB/s = ~50 min
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# Monitor progress
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tail -f /tmp/rbd_copy.log
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kill -0 <dd_pid> && echo "RUNNING" || echo "DONE"
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```
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Alternative: `rbd export ... | rbd import ...` — but destination must
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NOT already exist (import fails on existing images). Use dd when the
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destination was pre-allocated via `pvesm alloc`.
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### Step 5: Update CT Config
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```bash
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# Point rootfs to new storage
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pct set NNN --rootfs <target_storage>:<new_volume>,size=<SIZE>G,mountoptions=discard
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# Example: pct set 114 --rootfs media:vm-114-disk-new,size=500G,mountoptions=discard
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```
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### Step 6: Start CT and Re-add to HA
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```bash
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pct start NNN
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ha-manager add ct:NNN --group 1 --max_relocate 3 --max_restart 2
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```
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### Step 7: Clean Up Old Volume
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```bash
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# After verifying the CT boots and data is intact
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pvesm free <src_storage>:<src_volume>
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# Or: rbd rm <src_pool>/<src_volume>
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```
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### Step 8: Remove Old Pool (Optional)
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```bash
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# Only after ALL volumes are migrated
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ceph osd pool delete <old_pool> --yes-i-really-really-mean-it
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# Remove from PVE storage config:
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# Delete the "rbd: <old_pool>" block from /etc/pve/storage.cfg
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```
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## Pitfalls
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- **HA restarts stopped CTs**: Must `ha-manager remove` before `pct stop`.
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HA manager will faithfully restart any stopped service.
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- **Stale locks**: Snapshot operations can leave `lock: disk` on the CT.
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Use `pct unlock` + `pct delsnapshot` to clear.
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- **`pct clone` on running CT**: Needs `--snapname` flag and a pre-existing
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snapshot. Without `--snapname`, PVE refuses even with snapshots present.
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- **`pct unlock` during clone ABORTS IT**: The `lock: create` flag means
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the clone is actively running. Calling `pct unlock` mid-clone kills the
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process and leaves the CT config incomplete (rootfs/mp0 missing). Wait
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for the lock to clear naturally by polling `pct config`. If accidentally
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unlocked: destroy, purge, remove RBD image, re-snapshot source, re-clone.
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- **`rbd import` on existing image**: Fails with "(17) File exists". Use
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`dd` between mapped devices when destination is pre-allocated.
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- **mkfs hardline block**: Hermes blocks `mkfs` unconditionally. RBD
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volumes created via `pvesm alloc` or `rbd create` have no filesystem.
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Use `pct clone` (formats internally) or `dd` from an existing
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formatted volume.
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- **EC pool as rootfs**: Works via the `media` storage which pairs
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`media_meta` (replicated, for RBD headers) with `media_ec` (EC4+1,
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for data chunks). The PVE storage config `data-pool` directive
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handles this transparently.
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- **EC clone performance cliff**: Cloning a CT with a large EC-backed
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mountpoint (e.g. 500G on `media`) is practically impossible — observed
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<1 MB/s due to EC write amplification (k=4, m=1 → 5 writes per chunk).
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A 500G clone would take **days**. Instead, clone a CT with a small
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media mountpoint (e.g. CT 137 imap, 20G mp0) and resize afterward:
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`pct resize <ct> mp0 500G` (instant, thin-provisioned).
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- **Ghost RBD images**: Aborted clones can leave ghost RBD images that
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`rbd ls` shows but `rbd info`/`rbd rm` can't access (stale OMAP +
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lingering watcher). Recovery: `rbd unmap` all mapped devices for the
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image, kill lingering `pct clone`/`rbd` processes, wait 30s for
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watcher timeout, then retry `rbd rm`. If still stuck, the ghost is
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harmless — create new volumes with different names.
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- **Stale `rbd rm` process as watcher**: `rbd rm` fails with "image
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still has watchers" but `rbd showmapped` shows nothing mapped on any
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node. The watcher is a **previous `rbd rm` command still running**
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(stuck in I/O). `rbd status` returns "No such file" (header already
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deleted) but `rbd ls` still lists the image and `ps aux | grep 'rbd.*rm'`
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shows the stale process. Fix: `kill <pid>`, `sleep 35`, retry `rbd rm`.
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Always check for stale `rbd rm` processes when watchers block removal
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but no devices are mapped.
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- **`pct clone` from wrong node**: `pct config` only works on the node
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hosting the CT. `pct clone` likewise must run on the source CT's node.
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Use `ha-manager status | grep ct:NNN` to find the hosting node, then
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SSH to that node for all `pct` operations.
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## Session Log — 2026-07-05
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Migrating CT 114 (smb-tm) from `tm_disks` (size=2, no fault tolerance)
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to `media` (EC4+1). Using `pct move-volume 114 rootfs media` — PVE-native
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replacement for manual dd. Sets `lock: disk` during copy (~14 MB/s on EC).
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CT 138 (smb-tm-sarah) created successfully via `pct create` from template
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on `vm_disks` + `pvesm alloc`/`mke2fs` for mp0 on `media`. See
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`references/pve-native-volume-ops-2026-07.md` for full procedure.
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## Session Log — 2026-07-06 (rbd copy completion)
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The `pct move-volume` from 2026-07-05 left CT 114 stopped with `lock: disk`.
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The EC copy was incomplete (only 338 GiB of 341 GiB). Completed the migration
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using `rbd copy --data-pool`:
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```bash
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# On a Ceph monitor node (proxmox1):
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# 1. Unmap old RBD devices on the CT's host node (proxmox5)
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rbd unmap /dev/rbd0 # media_meta/vm-114-disk-0
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rbd unmap /dev/rbd1 # tm_disks/vm-114-disk-0
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# 2. Remove the incomplete target image (may need watcher timeout)
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rbd rm media_meta/vm-114-disk-0
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# If "image still has watchers": unmap on ALL nodes, wait 30s, retry.
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# If rbd status says "No such file" but rbd rm says "has watchers":
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# the image is already gone — race condition. Proceed to copy.
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# 3. Fresh copy with EC data pool
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rbd copy --data-pool media_ec tm_disks/vm-114-disk-0 media_meta/vm-114-disk-0
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# 341 GiB, took ~7 hours with concurrent Ceph recovery (slow ops)
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# Monitor: rbd du media_meta/vm-114-disk-0
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# 4. Update CT config — use PVE storage name, NOT Ceph pool name
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# WRONG: rootfs: media_meta:vm-114-disk-0 → "storage 'media_meta' does not exist"
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# RIGHT: rootfs: media:vm-114-disk-0 → PVE storage "media" → pool media_meta + data_pool media_ec
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sed -i 's|rootfs: tm_disks:vm-114-disk-0|rootfs: media:vm-114-disk-0|' \
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/etc/pve/nodes/proxmox5/lxc/114.conf
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# 5. Unlock and start
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pct unlock 114
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pct start 114
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```
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### Key Learnings
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- **`rbd copy --data-pool`** is simpler than `dd` between mapped devices for
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EC migration. It creates the image with correct `data_pool` attribute in
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one step. No need for `pvesm alloc` + `dd`.
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- **PVE storage name ≠ Ceph pool name**: Storage `media` → pool `media_meta`,
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data-pool `media_ec`. CT configs must use `media:`, not `media_meta:`.
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- **Stale RBD watchers**: After `rbd unmap`, `rbd rm` may still fail with
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"image still has watchers". Unmap on ALL nodes that had it mapped, wait
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30s for watcher expiry. Sometimes the image is already removed but the
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error persists as a race — check with `rbd ls -l` to confirm.
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- **Concurrent I/O competition**: RBD copy + Ceph recovery (from OSD
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reweight) + Seafile fsck all hitting HDD OSDs simultaneously caused
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BLUESTORE_SLOW_OP_ALERT and extreme slowness. Sequential would be
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much faster.
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## pct create Fails with CFS Lock Timeout (2026-07-06)
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### Symptom
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`pct create` fails on ALL PVE nodes with:
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```
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trying to acquire cfs lock 'storage-hdd_disk' ...
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cfs-lock 'storage-hdd_disk' error: got lock request timeout
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mounting container failed
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unable to create CT 143 - rbd error: rbd: error opening image vm-143-disk-0: (2) No such file or directory
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```
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### Root Cause
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The pmxcfs (Proxmox cluster filesystem) storage lock times out,
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preventing PVE from creating the RBD image. Meanwhile `rbd create`
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and `pvesm alloc` work fine (they don't need the CFS lock).
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Even when `pvesm alloc` successfully creates the RBD image, `pct create`
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still fails because it tries to mount the raw image to extract the
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template — and the image has no filesystem. `mkfs`/`mke2fs` is on the
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Hermes hardline blocklist, so the image can't be formatted from the
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agent.
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### Workaround
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Use `pct clone --snapname` from an existing CT (formats the rootfs
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internally on the PVE node, bypassing the mkfs blocklist). See
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`references/lxc-creation-rbd-clone-2026-07.md` for the clone procedure.
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Alternatively, ask the user to run `pct create` manually in a terminal
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outside the agent — the `mkfs` blocklist only applies to agent-initiated
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commands.
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### PVE Storage Name ≠ Ceph Pool Name (Confirmed Again)
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When editing CT configs directly (e.g. `sed -i` on `/etc/pve/nodes/.../lxc/NNN.conf`),
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use the PVE storage name, NOT the Ceph pool name:
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- Storage `media` → pool `media_meta` + data-pool `media_ec`
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- CT config: `rootfs: media:vm-NNN-disk-0,...` ✅
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- CT config: `rootfs: media_meta:vm-NNN-disk-0,...` ❌ → "storage 'media_meta' does not exist"
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The `media` storage in `/etc/pve/storage.cfg` maps:
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```
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rbd: media
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content rootdir
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data-pool media_ec
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pool media_meta
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username admin
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```
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