openzfs/zfs

MD RAID headers can cause Linux to steal disks from ZFS

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#634 opened on Apr 2, 2012

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 (30 comments) (0 reactions) (0 assignees)C (9,908 stars) (1,703 forks)batch import
Bot: Not StaleStatus: Understoodgood first issue

Description

I received a report from a veteran Gentoo user that MD RAID had stolen two disks from a raidz2 vdev. It seems that ZFS leaves a hole for a bootloader that an MD RAID header can occupy, causing this issue. This occurred on partitions that were 0xBF, not 0xFD.

I have found myself recommending people do mdadm --zero-superblock ... before creating a ZFS pool to avoid this situation. It would be a good idea to modify the code to zero this at vdev creation to preclude any possibility that an old MD RAID header will cause the kernel module to steal the disks.

I am not sure if I have time to do this right now, but I figured that I would file a report so that people are aware of the issue.

Contributor guide

Tech stack
c
Domain
backendinfrastructure
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C programmingLinux kernel conceptsZFS architecturemdadm utility
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
Investigate the vdev creation code in the ZFS source tree (likely in module/zfs/vdev.c or similar). The issue suggests zeroing the MD RAID superblock header during vdev creation to prevent Linux from stealing disks. Review the 30 comments on the issue for any pointers or proposed implementations. Look for existing tests or documentation related to disk initialization.