cc_resizefs does not allocate space on all disks of a multi disk btrfs volume

[ubuntu-server-builder]

This bug was originally filed in Launchpad as LP: #1955858

Launchpad details

affected_projects = []
assignee = None
assignee_name = None
date_closed = None
date_created = 2021-12-28T01:05:59.703006+00:00
date_fix_committed = None
date_fix_released = None
id = 1955858
importance = medium
is_complete = False
lp_url = https://bugs.launchpad.net/cloud-init/+bug/1955858
milestone = None
owner = nothing4you
owner_name = Richard Schwab
private = False
status = triaged
submitter = nothing4you
submitter_name = Richard Schwab
tags = []
duplicates = []

Launchpad user Richard Schwab(nothing4you) wrote on 2021-12-28T01:05:59.703006+00:00

cloud provider: self-hosted, proxmox

cloud-init config: growpart:   mode: auto   devices:     - /dev/sda1     - /dev/sdb1     - /dev/sdc1     - /dev/sdd1

I have a multi disk btrfs volume as root fs for the vm. Each disk needs to grow on first boot and the btrfs filesystem should be resized. Partitions are grown just fine and btrfs detects that, however, running btrfs filesystem resize max / as currently used in https://github.com/canonical/cloud-init/blob/bae9b11da9ed7dd0b16fe5adeaf4774b7cc628cf/cloudinit/config/cc_resizefs.py#L81 does not account for having multiple disks.

From the btrfs-filesystem man page (debian 11, Btrfs v5.10.1):

The devid can be found in the output of btrfs filesystem show and defaults to 1 if not specified.

Since a devid is not passed only the first disk will be resized, other disks will stay with "slack" space.

This is after I manually resized disk id 2 for testing, before it also had 3GiB slack:

root@test-vm:~# btrfs device usage / /dev/sda1, ID: 1    Device size: 4.00GiB    Device slack: 3.50KiB    Data,RAID10: 310.25MiB    Metadata,RAID10: 64.00MiB    System,RAID10: 8.00MiB    Unallocated: 3.62GiB

/dev/sdb1, ID: 2    Device size: 4.00GiB    Device slack: 3.50KiB    Data,RAID10: 310.25MiB    Metadata,RAID10: 64.00MiB    System,RAID10: 8.00MiB    Unallocated: 3.62GiB

/dev/sdc1, ID: 3    Device size: 4.00GiB    Device slack: 3.00GiB    Data,RAID10: 310.25MiB    Metadata,RAID10: 64.00MiB    System,RAID10: 8.00MiB    Unallocated: 640.73MiB

/dev/sdd1, ID: 4    Device size: 4.00GiB    Device slack: 3.00GiB    Data,RAID10: 310.25MiB    Metadata,RAID10: 64.00MiB    System,RAID10: 8.00MiB    Unallocated: 640.73MiB

[ubuntu-server-builder]

Launchpad user Richard Schwab(nothing4you) wrote on 2021-12-28T01:05:59.703006+00:00

Launchpad attachments: cloud-init.tar.gz

[ubuntu-server-builder]

Launchpad user James Falcon(falcojr) wrote on 2022-01-06T15:14:17.489796+00:00

Thank you for the detailed report. This is a use case we should support.