In this video, you'll learn about RAID devices. RAID configurations are pretty common on enterprise
hardware. The goal of RAID is to offer an array of independent disks. That's also where
it stands for Redundant Array of Independent Disks. And that is for increased redundancy.
If one of the disks fails, you still have storage left to take care of it. There are
different types of RAID. RAID 0 is striping. Striping means that you create one big disk
device out of multiple disk devices. In striping, you don't take care of redundancy. So if one
of the disks breaks, you're in trouble. RAID 1 is mirroring. So if one of the disks breaks,
then the other one takes over. RAID 5 is striping with distributed parity. And RAID 6 is striping
with dual distributed parity. RAID 5 and RAID 6 both are using different disk devices in
such a way that if one of the disk devices breaks, you still can continue using your
storage. Then there is RAID 10, which is a combination between mirrored and striped.
RAID devices can be purchased hardware-wise. You can also create software RAID devices.
That's what we are going to do here. If you want to, you can use either an entire disk
or you can put a partition in your RAID device. If you put a partition inside, then make sure
that you are setting the RAID device type. Next, you would use the mdadm command. MD
stands for multiple device and ADM, obviously, for administrator. You define the device that
you want to create, as well as the level, as well as the number of disks. Next, you
put a file system on it. You make the configuration persistent and you mount it. And finally,
you put everything in etcfsstep. And you can monitor the status of your RAID devices
through slashproc slash mdstat or using mdadm. Let me show you. As you can see in LSBOK,
I have added two more disks, NVMe 0, N4, and N5. And that is what I'm going to use in my
RAID configuration. So do we have mdadm? Yeah, we do have mdadm. And I am going to use it
to create the device md0. The level is one. RAID level one is a simple RAID mirroring.
So one of the disks is used as the backup of the other disk. RAID disks is two. And
then I need to mention my devices. So dev NVMe 0, N4, and dev NVMe 0, N5. So it is telling
us that this RAID device might not be suitable for booting. We don't talk about booting.
So that is OK. And I'm continuing to create the array. And you can see the device is already
started. So next, you put a file system on it. And then you create the configuration
mdadm, minus minus detail, minus minus scan. And you write that to the file etc mdadm.conf.
That will make sure that your configuration is persistent. And you can reinitialize your
RAID device. Then we need a mount point, so the RAID directory. And I'm going to mount
dev md0 on slash RAID. And now if I copy stuff to this RAID device, it will be stored
there. So if you want to make it persistent, you need to put it in etc fsstep. And in etc
fsstep, you are going to define your device. This time, dev md0 is OK, because the device
will be detected based on the metadata information that has been written to the hard disk. So
I'm mounting my dev md0 on slash RAID. The file system is just ext4. The mount options
are default and 0 and 0. And that will make sure that it is persistent. You want to know
what is going on? Well, have a look at the contents of proc mdstat, which is a proc file
that is giving synchronization information about your RAID device. Or alternatively,
use mdadm minus minus detail on your RAID device. Like this, this is giving a little
bit more detail about the current state. Now, when you are working with RAID devices, occasionally
you will have to replace a failing device. In order to do so efficiently, it's a smart
idea to have an unused RAID member as a hot spare. So when you are creating, you can create
this way with minus minus spare devices is one. And then you can fail a device. You can
do it manually to test if it is working. And after failure, you remove the device, and
then you add the device that was marked as a spare device previously. And that's how
you replace failing devices.