CentOS 6 add RAID1 partition

Toasterman · 02-08-2016, 01:18 PM

Hello,
When I installed CentOS 6 originally I had it set up with two 4TB drives in RAID1. I have the volumes set up as follows:

Code:

(parted) print free
Model: ATA ST4000DM000-1F21 (scsi)
Disk /dev/sda: 4001GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt

Number  Start   End     Size    File system  Name  Flags
        17.4kB  1049kB  1031kB  Free Space
 1      1049kB  4195MB  4194MB                     raid
 2      4195MB  5244MB  1049MB  ext4               raid
 3      5244MB  13.6GB  8320MB                     raid
 4      13.6GB  2178GB  2164GB                     raid
 5      2178GB  3184GB  1006GB                     raid
        3184GB  4001GB  817GB   Free Space

I am wanting to create another volume with the 817GB of free space at the end. However, I have not been able to find a straight-forward guide that shows what I need to do. I need to add an additional partition with the unallocated space, not create a whole new table. I do not want this to affect the existing partitions in any way. If this was a regular non-RAID partition it would be much easier.
Does anyone know of a guide that can show what I am trying to do here? Thank you.

trickykid · 02-08-2016, 01:56 PM

I'm assuming you want these to be separate from your existing RAID1, sort of mirrored on their own? If so..

You'll want to create a new partition (6) in your case (on both drives).

Code:

# parted /dev/sda
(parted) mkpart logical 3184Gib 4001Gib
(parted) set 6 raid on
(parted) align-check optimal 6

After you created your partition 6 on each drive device, you need to create an MD device and then add them to be mirrored:

Code:

# mdadm --create /dev/mdX --level=1 --raid-devices=2 /dev/sda6 /dev/sdb6

Where X in /dev/mdX is your new unused md device (some start at 0, some start at 126 or 127, just make sure to use one you aren't already using for the existing RAID1 setup). Get the existing ones by doing a:

Code:

# cat /proc/mdstat

Once you get your RAID1 going, you can format the device with whatever filesystem you prefer (ex. mkfs.ext4 /dev/mdX). Once it has a filesystem, you can mount it to start using it. (Also add to /etc/fstab to mount at boot time of course).

I'm also assuming the new partitions are devices sda6 and sdb6, you'll want to do an fdisk -l to make sure.

I'm doing most of this from memory so you might want to double check my commands. Always backup your data before doing these types of changes as well.

But those should be the basic steps in adding your unused disk space in it's own RAID1 mirror.