Wednesday, 27 May 2015 00:00

Recovering the GRUB on software RAID

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Recovering the GRUB on software RAID

The introduction: The software RAID 1 array consisting of 2 hard drives is used by default (if the system is set while ordering) on Hetzner root servers. What on earth made me a day or two ago reboot the server after 242 days uptime? After rebooting it never appeared on-line. Let's start from here. 1. At first, I decided to reboot once again, using https://robot.your-server.de/server this time.

b2ap3_thumbnail_groob-raid1.jpg

It didn't help.

1.Then I went to Support Service and wrote a humble letter. I learnt at the same time that there was no support for the root server software. Instead, I received a letter similar to this text:

we have connected a remote console to your server to solve the issue.Access details:http://lara03.rz13.hetzner.de

user: ******

pass: ******

Please note that access can only be guaranteed for a maximum of two hours. If the

Lara is not used after the ensured time period, we can use it elsewhere without

providing further notice.

2.I went to the above-noted address, entered the username and password. And I saw

b2ap3_thumbnail_groob-raid2.jpg

3."Yeah," I said, and began to do a Google search for «error: symbol not found: ‘grub_divmod64_full». I learnt that I was not alone with such a problem, and that the most likely cause had been the system update.

4.I loaded the server in alarm mode (make sure to select 64-bit, if you had a respective system installed)

b2ap3_thumbnail_groob-raid3.jpg

I do not want to keep you in suspense for a long time - the solution was as follows:

1.I created a chroot environment:

# mount /dev/md2 /mnt
# mount /dev/md1 /mnt/boot
# mount -t dev -o bind /dev /mnt/dev
# mount -t proc -o bind /proc /mnt/proc
# mount -t sys -o bind /sys /mnt/sys
# chroot /mnt

2.Then I reinstalled the GRUB:

# grub-mkconfig -o /boot/grub/grub.cfg
# grub-install /dev/sda
# grub-install /dev/sdb
# update-grub;

Here are a couple of comments. It seems that the boot loader should be installed on md1 (# grub-install /dev/md1), but this variant did not work, returning a number of errors. Therefore I had to install it on either of the two mirrored drives severally. I do not know if this was correct. But it helped in my case.

In conclusion, here are a couple of links to the posts of people with similar problems:

1.http://www.ivanov2.ru/error-symbol-not-found-grub_divmod64_full

2.http://blog.wolfspelz.de/2012/05/hetzner-root-server-does-not-boot-and

Last modified on Wednesday, 27 May 2015 15:52
Data Recovery Expert

Viktor S., Ph.D. (Electrical/Computer Engineering), was hired by DataRecoup, the international data recovery corporation, in 2012. Promoted to Engineering Senior Manager in 2010 and then to his current position, as C.I.O. of DataRecoup, in 2014. Responsible for the management of critical, high-priority RAID data recovery cases and the application of his expert, comprehensive knowledge in database data retrieval. He is also responsible for planning and implementing SEO/SEM and other internet-based marketing strategies. Currently, Viktor S., Ph.D., is focusing on the further development and expansion of DataRecoup’s major internet marketing campaign for their already successful proprietary software application “Data Recovery for Windows” (an application which he developed).

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