Boot with a degraded raid 5

ben.div ben.div at
Tue Dec 4 18:16:44 UTC 2007

Woh ! Absolutely nobody can help me on this question ? I've already 
asked about this on 4-5 lists or forums, and I've cumulated : 0 answer.
Where could I find help on this subject ? The kernel team ? Who has 
developped this part (boot on initramfs and device detection) ?

I'm stucked on that problem since 2 weeks. Please, help :)


Ben Ben a écrit :
> Hi all
> I have setup 2 software raids (5 and 0) with 3 hard disks (120, 160, 250
> Go) on my gutsy box. The raid 5 array (md0) contains the root system,
> and the raid 0 array (md1) is mounted as a storage (unused) partition.
> The /boot partition is a normal ext3 partition, present on each disk
> (duplicated manually, for the moment).
> I'm trying to let this setup boot, even if the raid 5 array (md0) is
> degraded (ie one disk fails). When all hd are present, the system boots.
> But if I try with only 2 disks, initramfs loads well, but md0 is never
> mounted so the system doesn't find / and stop loading.
> When the boot fails, the system gives me the hand in initramfs console.
> Here, I can run my md array with this command :
> # mdadm --assemble --scan --run
> The "--run" option tell mdadm to start array, even in degraded mode.
> So here, I suspected that the wrong option was passed to mdadm in
> initramfs, and tell it to not to run a degraded array.
> I've found (with grep on initrams content) that the file
> /etc/udev/rules.d/85-mdadm.rules contains this line :
> SUBSYSTEM=="block", ACTION=="add|change", ENV{ID_FS_TYPE}=="linux_raid*", \
>         RUN+="watershed /sbin/mdadm --assemble --scan --no-degraded"
> I guess it's the boot parameter for mdadm ! So, I changed it, made a new
> initramfs, reboot with only 2 disks and... nothing more, it doesn't
> start anymore :/
> So, after this long story (sorry), my questions :
> Do you think I'm totally lost, or editing this file is the good way ?
> Is there a good reason why ubuntu's dev chose this "--no-degraded"
> option for mdadm by default ?
> What can I do more ??
> Thank's for reading !
> Ben

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