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Archive for July 16th, 2009

Software RAID Ubuntu 9.04 Linux

by on Jul.16, 2009, under linux/ubuntu

Setting up software RAID is “fairly” easy. But first you must install the ALTERNATE installation CD for Ubuntu. (CentOS is pretty straight forward when you select “manual partitioning” in the GUI installer on the regular ISO).

Once you download and burn the alternate ubuntu ISO for your cpu architecture, boot it up on the machine you want to install. (Note: this will erase data on the drives, so make sure no external drives are connected, or any drives in the system you don’t want raided).

During the install, when you come to partitioning, select manual and delete the partitioning tables that currently exist on your drives so that each drive has “FREE SPACE” as the only option under the device.

I’m going to be setting up RAID5, which in my opinion is the best balance between performance and redundancy. (This box is going to be a media server / backup / desktop with three TB drives).

Now for my first device (HD) I’m setting up 3 partitions, (boot, root, and swap). I create the first primary partition of 100MB at the beginning of the drive and set the “use for RAID” where you might normally select ext3, boot, swap etc.  Also be sure to add the boot flag to this partition.

The second partition I setup as logical 6GB and “use for RAID” selected here as well. And the third I set the remainder as a primary partition and “use for RAID”.

I repeat these partitions on the remainder of the 2 drives so each of the 3 drives have identical partition tables.

Next we’re going to select “configure software RAID” that is at the top of the menu, and create a new MD (Multi Disk) device.

Keep in mind we have 3 partitions per disk, totalling 9. So we will have to create 3 MD devices in order to raid each partition.

Creating the first MD device we select RAID1 (mirroring) for the boot partition. This will allow the system to boot properly. (This single raid 1 is very important to our system functioning).

For number of active devices, we type in 3. And 0 spares. Selecting /dev/sda1, /dev/sdb1, and /dev/sdc1 in the device list.

We will repeat creating an MD for each “set” of partitions. (for a total of 3 times). But these subsequent partitions will be RAID5.

You will be presented with RAID MD devices showing up on the partition overview. This is when we will set these partitions to EXT3, SWAP etc…

The 100MB raid1 partition we will set up as EXT3 mounted at /boot. This raid1 will allow the system to boot and not throw a grub error 2 at us.

The 12GB raid partition will be set up as SWAP

And the 2TB partition will be set up as EXT3 mounted at root /

Once we have those set, we finish and write to partition table. It’ll format the drives, sync the arrays and install the OS.

After that’s all said and done it’ll want to reboot. And we’re finished!

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GRUB Error 2 Ubuntu 9.04 RAID

by on Jul.16, 2009, under linux/ubuntu

After installing software RAID, or perhaps for some other reason – you’re presented with a system that cannot boot properly. In my case, I installed a RAID5 Array and was presented with a GRUB ERROR:2 on boot.

GRUB Error 2 is basically “Selected Disk does not exist“.

Which likely means that grub is pointing to a disk or device that is either not recognized or as stated, doesn’t exist. It may be pointing to (hd0 0,1)  instead of (hd0 0,0) or whichever missconfig. In my case with the newly installed RAID, it’s likely the issue of GRUB being non-existant on subsequent disks, or not mapped properly to the MD array.

To fix this error after a RAID install, I had to go back in with the alternate installation CD and modify my RAID on the /boot partion (100MB).

Instead of this being a RAID5, I changed it to be RAID1 (mirroring) instead. So instead of 1 drive having the pairity value, the 3 drives now have an exact copy of the static boot files. We’re now able to boot our system!

Otherwise you may have to manually edit GRUB and change the device it’s trying to boot. (Such as mentioned above where it may be trying to boot into hd0 0,1 instead of hd0 0,0)

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