Unused Storage on Deployed Machines

Hey folks!

On an enlisted machine I have a number of physical disks. I commission the machine with ‘Preserve Storage Configuration’ as there is existing data I’ve pre-seeded for workloads after deployment.

To deploy, I have several physical disks, and used only one of those on the commissioned node (mounted as /) for deployment of the OS.

On the deployed machine, it’s my intention to mount the remaining disks post-deployment during a configuration pass. During my tests the remaining disks are visible to the OS (in lsblk, parted) but all have "Unrecognised disk label’ and “Partition Table: Unknown” in parted.

I had presumed that if I leave a disk unused in MAAS that it doesn’t get modified, but is this not the case?

I tested this theory out:

Commissioned a machine with several disks that had existing data on them, and selected ‘retain storage configuration’

Result: Disks are not manually mountable after deploy - parted gives ‘Unrecognised disk label’.

Repeated the test with another similarly setup machine, but with the disks disconnected until after deployment.

Result: Disks are mountable after reconnecting.

What does MAAS do to the disks?

MAAS instructs Curtin to wipe the superblock of all known disks. This is done in case the previous deployment uses the same labels as the new deployment and to prevent other conflicts. MAAS can only instruct Curtin to wipe the superblock for disks it knows about. Deleting the disk from MAAS will prevent them from being wiped.

Note: Disk erasing upon release erases all disks on the system regardless of whether or not they are modeled in MAAS.

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