Re: Debian kernel stanza after aptitude kernel upgrade

[Tim Small <tim@seoss.co.uk>]

On 21/09/10 11:39, A. Krijgsman wrote:
> Stupid me! I didn't check the menu.lst of my grub, and apperantly 
> aptitude rebuilded the initrd for the new kernel.
> The sysadmin I got the server managed to het the md device back online 
> and I can now access my server again trough ssh.

Once you've installed the extra disk, I think you need to stick the 
output of

mdadm --examine --scan

into /etc/mdadm/mdadm.conf

and then run

update-initramfs -k all -u

This isn't particularly well documented, so feel free to update the 
documentation and submit a patch ;o).  You shouldn't need to hard-code 
the loading of raid1 etc. in /etc/modules.



A good quick-and-dirty hack to check that a machine will reboot 
correctly is to use qemu or kvm.  The below should be fine, but to be on 
the safeside, create a user which has readonly access to the raw hard 
drive devices, and run the following as that user:

qemu -snapshot -hda /dev/sda -hdb /dev/sdb -m 64 -net none

The "-snapshot" will make the VM use copy-on-write version of the real 
block devices.  The real OS will continue to update the block devices 
"underneath" the qemu, so the VM will get confused easily, but it's good 
enough as a check check to the question "will it reboot?".


>
> #My menu.list for grub:

Err, if that's all of it, then I'd guess you're not using the debian 
mechanisms to manage it?  I'd probably switch back to using the Debian 
management stuff, it handles adding new kernels etc. fairly well.



> Since Grub loads the initrd-image from one of the two disks, if one 
> fails, it won't boot the md root device anyway right?
> Is it that whel /dev/sda fails, /dev/sdb becomes /dev/sda? (or must I 
> state that hd1 becomes hd0 when hd0 has failed?)

This is a bit of a pain with grub1 - grub2 handles it a bit better.  
With all BIOSes I've seen, if the first disk dies, the second disk 
becomes BIOS disk 0x80 (i.e. (hd0) in grub).  The workaround is to run 
grub-install twice, telling grub that hd0 is sdb the second time by 
manually editing /boot/grub/device.map  Once grub has loaded the kernel 
and initrd into RAM, then the md code should stand a reasonable chance 
of working out which drive is OK.


Tim.

> This because I would prefere a stanza that always boots up in degraded 
> mode, rather then in a panic kernel mode ;-)
> I have seen stanza's containing both disksk within one stanza, don't 
> know if this is old or still supported?
>
> Thanks for your time to read and hopefully reply!
>
> Regards,
> Armand
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