CompTIA Linux+ XK0-005 – Unit 06 – System Configuration Part 5

37. RAID Level

Raid. Level three is a striping with a Parity drive. So what does that mean to us? What it means is that I have 3234 drives that are storing the actual data as a stripe. Striping means filling each one up equally as much. And I have another drive whose job is to maintain Parity. Parity means that if I lose one of the striped drives, the data on the Parity drive drive would be capable of recreating what’s missing. So, in a way, by utilizing the Parity, we can rebuild what’s gone. Now, the downside is, if you lose the Parity drive, that might be okay, because as long as the other ones are running and functioning fine, you can replace it. But if you lost a drive and lost the Parity drive, you’re completely out of luck. So it’s just choices of what you have. It’s it’s not as common a solution as another Raid Level that we’re going to see called Raid Level Five.

38. RAID Level

Now, Raid level five functions the same way. We still call it a stripe with parity, but the parity is actually distributed amongst all of the disks. So now if a single drive fails, there’s not a parity drive to fail. If the drive fails, the parity information on the other drives involved can rebuild what’s missing. Now, that’s how you recover from it. But during the process, process of replacing the missing drive, that parity information can still be used to access the missing information.

So while you’re replacing a drive, it still is a viable source of being able to retrieve information. You’re not down, you didn’t suffer downtime, you didn’t suffer data loss. Now that’s a commonly used type of system. And to make this work, Raid Five means you have to have a minimum of three disks. And again, most systems limit you to a 32. Certainly some hardware solutions can have many more drives than that, but for software solutions, it’s usually three to 32 drives that can work together in parity.

39. Logical Volume Manager

Alright, now, how do you make these really cool volumes? How do you do this stuff we just talked about? That’s done through a tool called the LVM, or the Logical Volume Manager. It’s your means that you can use to create these virtual volumes. Now, with LVM and a virtual volume, you can then choose whatever you want as a solution. You can expand the volume right on the fly. That means add a new drive. You can create a volume that, as I said, is larger than the actual physical disk because it’s utilizing storage areas on another disk. Or you can use it to begin to create the multiple volumes that we just talked about.

In trying to come up with other solutions for redundancy or whatever else you want to deal with, the idea is that you create what’s called a Logical Volume Group, which is a way of looking at these multiple disks as a single unit. Or it could be multiple partitions on these physical disks that show up as a single unit. Now, that’s important because I could have each disk with four partitions that say and I could take one partition from each drive, call it a volume, take another partition from each drive, call it another volume. When you create it, you can stripe it. I mean, there’s a lot of those options that we just got through talking about. But when we’re done, the operating system sees a single volume physically, though, represented by multiple drives or multiple partitions.

40. Implementing LVM

All right, to be able to implement the LVM, if you don’t already have it installed, you have to install the LVM package. Then, of course, you have to physically have the disks installed. And from there, you’ll create your physical volumes. Now, to make those physical volumes, you can use a tool called Pvcreate physical Volume creation. You then have to create the volume groups. That’s another tool called VG. Create volume groups creation. And then you create the logical volumes, the things that we see with the LB create command.

And once you make those, you then have to format them. Well, formatting is easy. We already saw that tool, the mkfs. Now, I know that sounds like a lot of work, but it’s just normal physical volumes, volume groups, logical volumes. Format it, then guess what? That’s right. It’s Linux. You have to mount it. And if you want that to be seen every time you’re reboot the FS tab again, file edit it so that every time you reboot, that volume is ready to go.

41. Topic C: Device Management

All right, now we’re going to talk about device management. And this is kind of a precursory overview of what do we mean by device management? In other words, we’re going to try to take a little mystery out of that dev directory.

42. Devices

All right? So remember that most everything, if not everything, is considered to be a file. So if I wanted to write data to a device, it’s really writing it to a file. But we define those devices in the device directory. That was the reason for some of the easiness of creating Linux is that I didn’t have to have an application programming interface for every single device. Now, some devices are considered buffered or block transfers, some are considered non buffered or character. As an example, your mouse is pretty straightforward. It’s going to send a character at a time.

The X, the Y positions where it is on the screen, the click, that’s a character based type of a device. A hard drive. Well, that’s a good example of a block where I’m sending blocks of data. Now, the names buffered and non buffered or block in character can be misleading because I can have a USB storage device. A USB two one storage device usually shows up as a character based device, but I can still send a block of data to that character and vice versa. I can send characters to a buffered device. So you take it for what it means. It’s kind of a conceptual idea about the type of device and how the transfer occurs.

43. Sample Devices

Now, when we talk about devices, again, it’s more than just hard drives or these USB drives. Those are some of them. But a device, as we said, was a file that we’re writing things to. So we don’t have all those application programming interfaces or retrieving data from. And we generally will see a large collection of devices in the Dev folder. Now, I don’t want to go through every single one, but remember, a device device is an object that we represent as a file that I’m going to get sent data to or get data from.

And it could be something like the Dev random, that’s a random number generator. It could be that loopback that we talked about. It could be your wireless card, your wired network card. Those are devices. They’re PCI devices that are still a file or at least retreat them as such. But it could be USBs and all the rest of them, CDROMs and all those things. So when we talk about devices, we’re talking about the definition of an object that we treat as a file that we’re going to communicate to.

44. Demo – Exploring the /dev Directory

All right, I’m going to start off by going to my command prompt, and we’re going to take a tour of the device directory. So I’m going to, first of all, verify that I am the route. Makes this life a little bit easier. I’m going to clear the screen also just to get stuff out of my way. And we’re going to CD to the device directory. Now that I’m here, let’s take a look with our command LS LF. And we’re going to take a look at the device directory where we’re actually already here. So I don’t need to point that out there, but I do want to pipe it to the more command so that we can kind of see this bit by bit. Okay, so what we’re seeing here are a variety of different devices. Some of them that we’ve explored already.

Actually, very few we’ve explored. We did see a loop device that we created in a different location. Consoles, characters, CD ROMs, lots of loop devices. Let’s get into the hard drives here. There we go. SDA one and two. SDA Five. SDB, which is where we created that extra swap file, was actually on that physical drive. A lot of lines, TTY lines on the Ghost with lots of devices. Again, remembering that each of these look like files, but they exist to give us the configurations of what we need to be able to actually use a variety of hardware. Now what we’re going to do is echo the word hello to our screen just so you can see that one of the devices, the standard output, is our monitor.

And so we just kind of utilize that device with the echo command to send that out. But if we try to actually send this off to an actual device, so echo hello, redirect it to the device null, then we actually have sent our output to a device that is incapable of displaying it. So it’s really going nowhere because the null device is that it’s nothing, and there’s no way to recover that information because that’s the type of thing nothing is. I know it sounds a little too metaphysical, I suppose, but anyway, it’s just the plain old null location. Another device we talked about was one that allowed us to create random number or characters.

And so that was the device random. And what you see by putting in here is a way of creating eight characters, eight random characters that are going to display to my screen. But one of the issues that we had is that some of these characters, these ones that are little question marks, could not be interpreted by our standard output. And so the little question mark means that it was a non printable character. So those are some issues that you have to also worry about, is compatibility with the information. Now to kind of just show you what we mean by compatibilities or incompatibilities.

We’re going to try to open up Ice Weasel here for a moment and see if we can get out here to the Internet and go to this website that you’ll find in the listings here that’s designed to help you find those different types of hardware that are or are not compatible with Linux. So this is Tldp. org and I’m going to try HowTo hardware HowTo and hit enter. And here we go. The hardware compatibilities list for us and its job is if I go through here to talk about the different processors, memory controllers, scuzzy Ray controllers, IDE, sound cards, hard drives and the idea is that if you click on any one of these like supported sound cards that it should show you all of those sound cards.

That should be working just fine with Linux, which is probably going to be most of the ones that you would find in any generic store or online location. So whether you go to a brick and mortar building or you go somewhere online and order any of these, I’m scanning through it very quickly. You shouldn’t have any problems with utilizing the hardware in today’s environment. But again, it’s just making sure that you understand as you’re looking at your devices and discovering what’s out there, that you can also go to a site like this, the compatibility, or just go to the vendors website itself and make sure that it is compatible with whatever version of Linux that you’re going to install it on.

45. Viewing USB Devices

Now, one of the most common types of devices we use today is a USB device. So there is a special command that lets you look at all of the USB attached devices that you have, and it’s simply called lsusb. Well, we know LS is a listing device. lsusb just means I want to see the USB devices. Now you have some options like the dashv to make sure that you see them in verbose mode code. Verbose just means tell me everything about the device and it’s going to get this information out of a specific location. The file that it’s stored in is in the procbusbases file. Suddenly here’s a new folder section we haven’t talked about. So that’s why we’re giving it to you. We’re telling you where you would go if you didn’t want to use the lsusb command. You can just ago look at the devices file.

46. Demo – Viewing Devices on the USB Bus

All right, we’re going to take a look basically at devices on the USB hub. And just so you can see this, I’ve plugged into one of the hubs a little USB stick and I double click it. You can see it open up. That will remember some of the things we set up with Linux that will automatically recognize and install certain hardware for you. So you don’t have to mount these drives each time you put them in or take them out. So we’re going to use the lsusb to see the basic information about the devices that are connected. And we can see in bus one, it talks about having a one one route, 20 route. And over here I have another device like Sarmedia, which is by the way, the device that I have on the setup. That is the crucial that you see here.

So what’s kind of important here is bus one. Bus one, device one says that it’s just a hub basically waiting for something to be plugged in. Bus two, device one is also the hub. This is actually on the front of my PC waiting for a device. And here is one of those devices plugged in. So that’s why you see bus number two. But either way, that’s not all that great information. So you might use the lsusb health to see what other options you have. And there you can see that I could choose only specific devices on the bus or show only devices with a vendor and product ID, or select the device or dump the hierarchy as a tree or show the now capital V is the version versus lowercase B, which is the verbose, which as it says, increases verbosity.

And it really does, it’s like four or five pages long. But let’s try the T here to dump the physical USB hierarchy as a tree. So we’re going to use the Lsusbt for tree and now we can kind of see the design as a tree. So bus two has this device too. We know its product by its hexadecimal value, but unless you have memorized those or you’re going to go out there and figure that out, it’s pretty hard to determine that this Lexmar crucial drive. Now again, bus two, bus one for the hubs, any way of plugging things in. So nothing too exciting there. While it will do the US LS USB with the dashv, I’m going to actually do this command twice because the first time it’s just going to blaze across the screen. Watch.

Okay. And you probably don’t even know how many pages I went through. So I’m going to pipe that into the more command so I can see it one page at a time. Now one page at a time is certainly a little nicer for us, I think. So you can actually look through, especially when it’s showing us bus number two first. Here it is, the Lexar media. So that certainly was more useful to see that information than it was to look at hexadecimal values and the manufacturer, it says, is crucial product serial numbers, probably the verbose. Remember, lowercase V was a little more useful for your needs. And now I can hit the space bar, but we know the rest of these are just hubs, so I’m going to hit Q for quit to go through there.

All right, let’s clear off the screen. And finally, let’s use the cat program to spit out to our screen the information we see under the proc bus USB devices file. And remember, this might be different, this path with the different distributions of Linux, but here I want to see the content of the devices file, which should have, I hope anyway, some detailed information about our USB devices. And again, it looks like this thing kind of scrolled along our screen, which is fine. I’ll scroll up a little bit. I’ll just move this over so I can get to this scroll bar. Because we know that our bus two was the first one that I brought up. So here it is, the controller.

Right? Again this information is telling me that this is the controller for that first bus, or for bus number two anyway. And then here’s what’s plugged in, which is again, that crucial drive. And again, it’s just a nice way to be able to get ideas of what’s plugged in, how much information is actually available to you through the command line in reporting the devices that are discovered. It’s not just simply what you see here on screen, which is a nice little picture of an external drive with the drives volume label that I double click and I see some files on. So it’s actually more to the information discovered by our systems. One of the nice things about Linux is you’re allowed to see everything pretty much that the operating system sees.

47. Viewing PCI Devices

Your PCI devices that could be your wireless cards, your network cards, the wired ones, or anything that we would call a plug in device are also devices that you can be listed with the command LS PCI. And it too has a verbose mode as well. Or you can go into the same location, nearly the same location under the Slash Proc Bus PCI. Now, USB devices and look at that file that just tells you about what’s been found, what’s been defined, what’s hooked up to your current system.

48. Unit 06 Review

All right, so in this unit what we did is we talked about these system devices, we talked about specifically hard drives, creating partitions, talking about volume, some rate options that you have, some file system extras like quotas. We went in from there and talked about specific swap partitions, swap files and then we gave you kind of an overview. We could almost say a little bit of what’s to come still in this course to talk about the types of devices, USBs, PCIs, where you would find them, how you can list them. But we are going to talk about some of those in some more detail, especially network cards and other types of PCI devices. But our goal was to get us started on what we can do. And I hope you see a lot of great flexibility and capability out of this Linux operating system just when it comes to your storage capability.

• Category: Uncategorized