RBD pool not starting "An error occurred, but the cause is unknown"

6 Feb 2026

      Hi all,

I've been battling this for about a year now.  I've deployed virtual machine hosts running AlpineLinux 3.23 (recently updated from 3.21) which ships `libvirtd` 11.10.0, Ceph 19.2.3 and QEMU 10.1.3.  (For reference: previous thread is archived at https://www.spinics.net/linux/fedora/libvirt-users/msg14421.html)

I have two RBD pools defined: one is a "high availability" pool which replicates a copy of each block on every node, the other (previously used with OpenNebula) just makes sure there are at least 2 copies of blocks across the nodes (preferrably 3).  They're called "ha-images" and "opennebula-images" respectively.

"ha-images" starts without issue.  It has a configuration like the following:

```
<pool type="rbd">
  <name>ha-images</name>
  <uuid>6beab982-52b3-495b-a4a7-ab7ebb522ef5</uuid>
  <capacity unit="bytes">16003182362624</capacity>
  <allocation unit="bytes">184657756160</allocation>
  <available unit="bytes">6658209792000</available>
  <source>
    <host name="172.31.252.1" port="6789"/>
    <host name="172.31.252.2" port="6789"/>
    <host name="172.31.252.5" port="6789"/>
    <host name="172.31.252.6" port="6789"/>
    <host name="172.31.252.7" port="6789"/>
    <name>ha</name>
    <auth type="ceph" username="libvirt">
      <secret uuid="c14a16b5-bba5-473a-ae9b-53a9a6b0a4e3"/>
    </auth>
  </source>
</pool>
```

No issues with it, it starts just fine.  "opennebula-images" never starts, its configuration:

```
<pool type="rbd">
  <name>opennebula-images</name>
  <uuid>fcaa2fa8-f0d2-4919-9168-756a9f4ad7ee</uuid>
  <capacity unit="bytes">16003182362624</capacity>
  <allocation unit="bytes">7893286499025</allocation>
  <available unit="bytes">6658213388288</available>
  <source>
    <host name="172.31.252.1" port="6789"/>
    <host name="172.31.252.2" port="6789"/>
    <host name="172.31.252.5" port="6789"/>
    <host name="172.31.252.6" port="6789"/>
    <host name="172.31.252.7" port="6789"/>
    <name>one</name>
    <auth type="ceph" username="libvirt">
      <secret uuid="c14a16b5-bba5-473a-ae9b-53a9a6b0a4e3"/>
    </auth>
  </source>
</pool>
```

The `libvirt` user I created in Ceph is able to list the RBD pool:

```
lithium:~# rbd --id libvirt ls -p one | head
gapmx-old-vda
gapmx-old-vdb
gapmx-testing-vda
gapmx-testing-vdb
gapmx-vda
gapmx-vdb
mastodon-vda
mastodon-vdb
mastodon-vdd
mastodon-vde
```

Starting it, `libvirt` merely tells me: "An error occurred, but the cause is unknown".  No logs written anywhere, no explanation.  Just "computer says no".

Yet, if I hand-configure my virtual machines, I can still mount RBD volumes as virtual disks within either pool.  I just can't browse them via `virsh` or `virt-manager` on the `opennebula-images` pool like I can for the `ha-images` pool.

Where should I be looking for the error?  What did I do wrong that makes it refuse to start?

me＠vk4msl.com

Ján Tomko

Stuart Longland VK4MSL

Michal Prívozník

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