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Re: Recovery from hard drive failure



OK, steps 1-3 went fairly smoothly.  Now, however, I'm unable to get grub-install to work.  When I do the following:

mount /dev/sda1 /newboot
grub-install '(sd0,0)'

I get the error message:

/usr/sbin/grub-probe: error: cannot find a device for /boot/grub (is /dev mounted?)

I get the same when I do grub-install /dev/sda1 .  Clearly, I have not done some crucial preparatory step for installing grub from the live rescue CD to the new hard drive's partition.  Any suggestions?

Thanks in advance,
-PT

On Fri, Nov 12, 2010 at 12:46 PM, Peter Tenenbaum <peter.g.tenenbaum@gmail.com> wrote:
Hi again --

As I'm studying the situation, my plan for how to do this recovery has evolved a bit.  What I'm planning now is the following:


1.  Install the new hard drives
2.  Boot off the rescue CD
3.  Use fdisk to set up one of the drives as the system / boot drive, with 3 DOS-style partitions (boot, swap, and everything else)
4.  Install grub in the boot partition
5.  Recover my backup to the new system disk via restore
6.  Update /etc/fstab to match the configuration I set up in (3) and (4), since I'm not setting up the new hard drives exactly the way that the old drive was configured
7.  Follow the instructions at http://linuxconfig.org/Linux_Software_Raid_1_Setup to incorporate the system disk and the second disk as a RAID-1 array.

If anyone wants to jump in and shout, "No, you fool!" when they see this plan, let me know.

Mark -- I've decided against using LVM because (a) it adds another level of complication to the overall recovery / RAID-ification procedure, which at my low level of expertise I really do not need, and (b) it's not clear to me that LVM offers that much benefit for a relatively simple home system with more hard drive capacity than I really need.  Maybe on my next system...

-PT


On Thu, Nov 11, 2010 at 11:01 AM, Peter Tenenbaum <peter.g.tenenbaum@gmail.com> wrote:
Klistvud -- excellent, thanks, that is definitely the way to go!  I can see that the rescue CD from live.debian.net (actually from cdimage.debian.org/cdimage/squeeze_live_beta1/amd64/iso-hybrid/) contains everything I need, so I'll use that.

Now:  in the interim, I've decided to take this opportunity to make my system RAID-1, so that I get an extra level of protection and also so that if I ever have another drive failure I can limp along on the other drive for the few days it will take me to get myself organized to recover.  Also, I get to set up a RAID-1 array, which I don't yet know how to do, and learning is fun.  As I understand it, the steps I need to take are:

1.  Install the new hard drives
2.  Boot off the rescue CD
3.  Use fdisk and mdadm to set up the 2 drives as a RAID-1 array
4.  Use LVM (or fdisk?) to partition the resulting array (boot, linux, and swap)
5.  Recover my backup to the array via restore command.

So now, a few new questions:

1.  Is the list above generally correct?
2.  When I installed Debian back in the summer I let the install script handle the disk partitioning.  This time I have to do it manually.  What size should I use for the boot and swap partitions?
3.  Do I need to manually install and configure grub in order to make the RAID-1 array the boot disk?  Again, this was handled for me by the installer script the first time around.
4.  What, if anything, do I need to do so that the RAID-1 array is activated at boot time?

Whew!  Sorry for the huge stack of questions, any and all help, encouragement, etc, is welcome!

Thanks in advance,
-PT


On Thu, Nov 11, 2010 at 8:16 AM, Peter Tenenbaum <peter.g.tenenbaum@gmail.com> wrote:
Hi everyone -- a few days ago the hard drive in my home Debian system started making unhappy noises and refuses to boot.  I discussed the situation with knowledgeable people and they diagnosed that indeed the hard drive had failed and needs replacement.

I have a recent backup of the hard drive which I made using dump, and I have a new hard drive on order.  My recovery plan is as follows:

1.  Burn a new netinst CD from a recent build (I am running Squeeze, btw)
2.  Replace the hard drive
3.  Use the netinst CD to set up the filesystem on the new hard drive
4.  Recover the backup using restore.

Here's my question:  should I allow the netinst CD to install Debian on the new hard drive, given that I plan to use restore to restore everything and thus would overwrite any new installation?  I realize that I can probably tune the action of the restore command so that it only restores what I need from the backup and doesn't touch a new OS install; but I think that the process of making the decisions for what needs to be restored and what does not would be complex, time-consuming, and error-prone; so I would rather just restore the whole thing.

Any advice you can offer would be welcome. 

Thanks in advance,
-PT




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