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docs/pbs-deployment: note ZFS case-insensitive + NFSv4 incompatibility

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Discovered during Phase 1.3 (mount NAS datastore). The Debian NAS's
/mnt/backup is on ZFS with casesensitivity=insensitive; NFSv4 writes
fail with EACCES even for root with no_root_squash. Known-bad
combination at the ZFS-on-Linux + NFSv4 layer.

Workaround: mount the NFS share with vers=3. PBS's chunk-based
access pattern works fine over NFSv3.

Added a section 0.5 to Phase 0 documenting the issue + both fixes
(quick: use NFSv3; cleaner: create case-sensitive child dataset).
Future deployments against this NAS won't rediscover the same wall.
This commit is contained in:
Vuong Hoang
2026-04-22 11:26:17 -07:00
parent 58f2a22966
commit 2f76da2108
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docs/runbooks/pbs-deployment.md
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@@ -63,6 +63,36 @@ so Cockpit doesn't clobber it.
Not blocking PBS work but worth tightening during a Cockpit pass —
reduce to `10.0.0.0/8` or more specific. Open item, not blocker.
### 0.5. ZFS case-insensitivity breaks NFSv4 writes
The Debian NAS's `/mnt/backup` is a ZFS dataset with
`casesensitivity=insensitive`. ZFS + NFSv4 + case-insensitive dataset
is a known-bad combo: lookups/readdir work, `create`/`write` ops fail
with EACCES even for root with `no_root_squash`.
**Workaround:** mount with NFSv3 instead of NFSv4. Update the VM's
`/etc/fstab` filesystem type to `nfs` and options to `vers=3`. PBS's
access pattern (dedupe chunks are writen-once/read-many) works fine
over NFSv3.
Example `/etc/fstab` line that works:
```
10.250.50.50:/mnt/backup/pbs-ana /mnt/pbs-datastore nfs defaults,_netdev,bg,hard,timeo=600,retrans=2,vers=3 0 0
```
**Cleaner long-term fix** (not required, but nicer): create a
case-sensitive child dataset for PBS's data:
```
sudo zfs create -o casesensitivity=sensitive -o mountpoint=/mnt/backup/pbs-ds \
NASPool/backupStore/pbs-ds
```
Then export/mount `/mnt/backup/pbs-ds` via NFSv4 as originally planned.
Case-sensitivity can't be changed on an existing dataset, which is why
the parent is stuck on case-insensitive.
## Phase 1 — Provision PBS-ANA (VM on pfi-pve)
**Target state:** a fresh Debian 12 VM on pfi-pve running