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Re: RAID 5 questions (software)

On Thu, Jul 07, 2005 at 01:34:15PM -0500, Michael Martinell wrote:
> On Thu, July 7, 2005 11:11 am, Andy Smith said:
> >> If the first hard drive crashes how do you recover?
> >
> > You restore from backups or do a new install.
> >
> There has got to be a better solution than that.  I never want to consider
> my backups to be a first line of defense against hardware failure.

I read it as how to boot a machine that has lost the only device that
has its /boot and root filesystem on.

If in actual fact the only filesystem missing is /boot then it may
well be possible to boot with a rescue cd like knoppix with a new
clean drive put in, make a new /boot on that, copy a kernel (and
possibly initrd) in, adjust /boot/grub/menu.lst to be correct and

But hopefully you can see how much hassle that is compared to
putting /boot and swap on a raid1 and suffering only the downtime
required to put a new disk in.

> Sources used:
> http://www.tldp.org/HOWTO/Software-RAID-HOWTO-5.html
> debian mailing list
> In that spirit I have set up the following:
> Debian 3.1r0a
> IDE 1-4 each with a 2 GB and a 38 GB RAID configured using Debian software
> RAID tool
> RAID 1 = 2 GB ext3 /boot (from disks 1 & 3)

This is massive btw, 100MB is generous for /boot, although
admittedly that does leave you with 2GB minus 100MB on disks 2 and 4
that may be hard to find a use for.

> RAID 1 = 2 GB swap (from disks 2 & 4)
> RAID 5 = 114 GB ext3 / (from disks 1,2,3,4)
> Results:
> If I replace hard drive 1 I am unable to boot.  Using the grub boot disk
> and pointing at hd 2,0 generates the following messages:
> md2 No spare disk to reconstruct array! continuing in degraded mode
> EXT3-fs: unable to read superblock
> pivot_root: No such file or directory
> /sbin/init: 432: cannot open dev/console: No such file
> Kernel panic: Attempted to kill init!
> How do I get the OS to recognize the spare disk now, after the failure? 
> If the RAID 1 was truly working would it have not booted?  Is there
> another setting on my boot floppy that would help here?

Hmm, I am not sure what is wrong here -  provided you have done the
grub-install to both disk 1 and disk 3 it should be OK.  But it
seems like it does get past booting and gets stuck having no root
fs, so that suggests something fundamentally wrong.  Try posing this
one on linux-raid list?

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