BootDegradedRaid

Revision 8 as of 2008-05-30 20:32:31

Clear message

Summary

This specification defines a methodology for enhancing Ubuntu's boot procedures to configure and support booting a system dependent on a degraded RAID1 device.

Rationale

Ubuntu's installer currently supports installation to software RAID1 targets for /boot and /. When one of the mirrored disks fails, and mdadm marks the RAID degraded, it becomes impossible to reboot the system in an unattended manner.

Booting Ubuntu with a failed device in a RAID1 will force the system into a recovery console.

In some cases, this is the desired behavior, as a local system administrator would want to backup critical data, cleanly halt the system, and replace the faulty hardware immediately.

In other cases, this behavior is highly undesired--particularly when the system administrator is remotely located and would prefer a system with redundant disks tolerate a failed device even on reboot.

Use Cases

  • Software RAID is often a less expensive alternative to Hardware RAID, and is always available on any Ubuntu system with multiple disk devices
    • This is particularly useful on low-end and small-form-factor servers without built-in Hardware RAID, such as blades and 1-U rack mount systems
  • RAID1 (mirroring) is currently a convenient mechanism for providing runtime failover of hard disks in Ubuntu
  • Remotely administered systems where the owners have taken the initiative to use dedundant disks in a RAID1 configuration expect to be able to boot even after a RAID degradation event

Scope

The scope of this specification is to solve this problem within Ubuntu's software raid support and default bootloader within the Intrepid Ibex development cycle.

Design

Implementation

Outstanding Issues

BoF agenda and discussion

References