So my OpenMediaVault (OMV) NAS did reboot today for some reason. It didn’t manage to boot up successfully again, however, but entered “emergency mode” instead.
After some digging around it seems this is related to the combination of LUKS drive encryption and MergerFS (same with UnionFS).
For normal operation, first the LUKS drives need to be decrypted. Then the decrypted drives can be pooled together with MergerFS.
Some changes in OMV 5 (as compared to OMV 4) cause the boot sequence to enter emergency mode if not all drives in
/etc/fstab can be mounted while booting. Since the LUKS drives are still encrypted when booting, mounting those drives obviously fails. And consequently mounting the MergerFS filesystem also cannot succeed.
The issue can be patched by adding the
nofail option to all LUKS drives in
/etc/fstab and also adding the
noauto option to the MergerFS entry in
/etc/fstab. It may only be a matter of time until OMV decides to rewrite
/etc/fstab, thus nullifying the changes described above.
But since I do not reboot my NAS that often, the above patch works fine for now.