Take the 2-minute tour ×
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It's 100% free, no registration required.

I'm a complete newbie to Ubuntu, but so far, I've had no luck installing a software RAID5 with Ubuntu. I've already installed Ubuntu Server 11.04 about 3 times. I followed the software raid instructions here to the best of my abilities, even though the screens are different. I did not use a RAID 1 for my boot partition on each drive...is that a must?

Anyway, I've had errors in past installations, but I was able to get through the entire install with 3 drives, a small bootable partition on each (sda/b/c1?), a swap partition on each (sda/b/c3), and then a large partition mounted to / for my RAID 5 (sda/b/c2). The final install step looks like everything works correctly because Ubuntu says it is installing GRUB to /dev/sda1 through /dev/sdc1, but then when I try to boot for the first time, it immediately says "error: no such disk GRUB recovery>".

I was able to login using LiveCD and try to get Grub loaded, but I haven't had any luck there as well. If I apt-get grub and run it and issue find /boot/grub/stage1, it says nothing is found. What am I doing wrong, how do I get to a working Raid5?

share|improve this question
add comment

2 Answers

I did not use a RAID 1 for my boot partition on each drive...is that a must?

In the instructions immediately under the installation section's first image, there is a warning in bold that states:

Warning: the /boot filesystem cannot use any softRAID level other than 1

I assume this is where things may be going wrong.

This is one reason why I stick to hardware RAID controllers as opposed to software - less chance of user errors, less chance of corruption, etc. :)

share|improve this answer
1  
I guess my problem is that I'm not willing to go out and drop a grand on a hardware RAID for my home NAS. –  Ed B May 24 '11 at 15:02
    
So, I've tried creating a software RAID 1 for the first partition, and designated it as a boot partition, but I'm not even able to install the filesystem now. Ubuntu gives me a big red screen saying there's been a problem and logs it. Why is this so difficult? Also, the tutorial for creating a softRAID is done for pre-10 I believe, so the options have changed, and it kind of glosses over some of the steps necessary to create the RAID. It would be helpful to have an updated and step-by-step guide to creating this, otherwise I spend a lot of time flailing. –  Ed B May 24 '11 at 15:05
    
@Ed B - Well i'm not too familiar with the soft-raid configurations, but what if you burn a pre-10 CD of Ubuntu, install it as per the config, then upgrade it? Not sure if this would help, but may be worth looking into. –  Jason May 24 '11 at 17:37
    
@Ed-b - Check out this link: $280 8-tray raid tower (edited, wrong link!) –  Jason May 25 '11 at 17:05
add comment

Software RAID is great once you get it going. It also means you can move your disks to another server which does not have the same hardware RAID card in it.

Why don't you set up your disks as follows.

Each disk gets 3 partitions, a small 10GB "scratch" partition that never gets used, a 30 GB Partition for Ubuntu RAID1, and for the 3rd partition use about 99% of the rest of the disk,leaving a small amount of free space. The 3rd partition will be used to set up RAID5 once you've installed Ubuntu.

Make ALL your disks have the same partition setup (use sfdisk to copy the partition layout by booting into Ubuntu Rescue Remix CD or other live CD image- you may want to disable RAID when you are doing this copy otherwise the live CD finds the RAID and makes it active- it can be a pain to unmount and then disable the mdX RAID array).

Here is the logic to this:

  • 1st "scratch" partition is there in case you are doing recovery and need a temporary FS for recovery (e.f. ddrescue recovery log). Or you can install a new OS onto it if you want.

  • 2nd partition is RAID 1 for Ubuntu. Set up /=2GB, /usr=6GB, /var=3GB, /home=3GB, /tmp=10GB (/tmp can be smaller but 10GB allows 1 full 8GB DVD image + some spare)

  • The various filesystems act as "firewalls" in case something fills up a FS, it is easier to recover and may not crash the system.

  • You can install LVM onto this RAID partition as well for added flexibility. Grub2 will boot from LVM on RAID1. I am using this. With LVM you set up LVs (logical volumes) for each filesystem.

  • No need for a separate /boot filesystem. This just complicates matters!

  • LVM provides flexibility as you can extend a filesystem easily or even migrate it to a new drive while the system keeps running.

  • Once Ubuntu is installed on RAID1 set up RAID 5 on the other disks.

  • You can boot into Ubuntu Rescue Remix CD and use "sfdisk" to nicely copy disk partitions from one to another. Better than dd 'cos it keeps the original drive geometry and size etc.

  • Don't use up 100% of the free space on the drive for RAID5. Keep 1GB ior so spare at the end of the disk. Future drive purchases from different drive manufacturers may be 10MB smaller than another which is "the same size". RAID then won't set up.

  • Use an "intent bitmap" for your RAID devices. This means if you get a crash, then only the recently written blocks are resynched.

  • set bootdegraded=true in your Grub2 boot parameters (in /etc/default/grub)

  • Don't forget to run grub-install /dev/sdb and /dev/sdc and /dev/sdd because you'd like to boot even if sda dies

I am sorry I can't give you exact steps as I have not use the new Ubuntu installer. You may be better off with the text-based one rather than the GUI.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.