IT Tips and Tricks

Assumptions:

Lets say you rented a server in Hetzner and it offers the wappy 4 x 10TB disks. You want the following disks configuration:

Disks: 1 and 2 (in RAID 1) total 10TB in Mirrored RAID 1 mode
Disks: 3 and 4 (In RAID 1) total 10TB in Mirrored RAID 1 mode

HOWTO:
1 – During the configuration of the Hetzner Linux Image you disable(comment out ‘#’) the disk3 and disk 4 from the configuration and set the RAIDLEVEL to 1. You can also decide what kind of partitions the first RAID disks will be setup here (in the section which starts with ‘PART’ lines)but this HOWTO doesn’t cover that.

2 – Save and let the system be built.

3 – After reboot run the following command:
lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT

Example Output:

<PRE>NAME SIZE FSTYPE TYPE MOUNTPOINT
sda 9.1T disk
|-sda1 8G linux_raid_member part
| -md0 8G swap raid1 [SWAP] |-sda2 512M linux_raid_member part |-md1 511.4M ext3 raid1 /boot
|-sda3 9.1T linux_raid_member part
| -md2 9.1T ext4 raid1 / -sda4 1M part
sdb 9.1T disk
|-sdb1 8G linux_raid_member part
| -md0 8G swap raid1 [SWAP] |-sdb2 512M linux_raid_member part |-md1 511.4M ext3 raid1 /boot
|-sdb3 9.1T linux_raid_member part
| -md2 9.1T ext4 raid1 / -sdb4 1M part
sdc 9.1T disk
sdd 9.1T disk </PRE>

You can see that the first partitions have been set under md0, md1 and md2 disks partitions BUT the drives sdc and sdd are not assigned to any RAID group. We will assign them to md3 with the command:

mdadm --create --verbose /dev/md3 --level=1 --raid-devices=2 /dev/sdc /dev/sdd

Result:

mdadm: Note: this array has metadata at the start and
     may not be suitable as a boot device.  If you plan to
     store '/boot' on this device please ensure that
     your boot-loader understands md/v1.x metadata, or use
     --metadata=0.90
 mdadm: size set to 9766305792K
 mdadm: automatically enabling write-intent bitmap on large array
 Continue creating array? y
 mdadm: Defaulting to version 1.2 metadata
 mdadm: array /dev/md3 started.

To verify we run the command:

lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT

Output:

<PRE>NAME      SIZE FSTYPE            TYPE  MOUNTPOINT
 sda       9.1T                   disk
 |-sda1      8G linux_raid_member part
 | -md0     8G swap              raid1 [SWAP] |-sda2    512M linux_raid_member part |-md1 511.4M ext3              raid1 /boot
 |-sda3    9.1T linux_raid_member part
 | -md2   9.1T ext4              raid1 / -sda4      1M                   part
 sdb       9.1T                   disk
 |-sdb1      8G linux_raid_member part
 | -md0     8G swap              raid1 [SWAP] |-sdb2    512M linux_raid_member part |-md1 511.4M ext3              raid1 /boot
 |-sdb3    9.1T linux_raid_member part
 | -md2   9.1T ext4              raid1 / -sdb4      1M                   part
 sdc       9.1T linux_raid_member disk
 -md3     9.1T                   raid1 sdd       9.1T linux_raid_member disk -md3     9.1T                   raid1</PRE>

Now we can start formatting the md3 disk array to ext4 format:
mkfs.ext4 /dev/md3

Create a mountpoint in the filesystem:
mkdir /DATA

Configure the /etc/fstab for mounting it at boot time:

mcedit /etc/fstab

Content:

proc /proc proc defaults 0 0
 /dev/md/0 none swap sw 0 0
 /dev/md/1 /boot ext3 defaults 0 0
 /dev/md/2 / ext4 defaults 0 0
 /dev/md3 /DATA ext4 defaults 0 0

Mount all existing drives set in /etc/fstab

mount -a

Verify the space in system:
df -h

Result:

Filesystem      Size  Used Avail Use% Mounted on
 udev             16G     0   16G   0% /dev
 tmpfs           3.2G  588K  3.2G   1% /run
 /dev/md2        9.1T  1.1G  8.6T   1% /
 tmpfs            16G     0   16G   0% /dev/shm
 tmpfs           5.0M     0  5.0M   0% /run/lock
 tmpfs            16G     0   16G   0% /sys/fs/cgroup
 /dev/md1        488M   40M  423M   9% /boot
 tmpfs           3.2G     0  3.2G   0% /run/user/0
 /dev/md3        9.1T   80M  8.6T   1% /DATA