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Book Chapter 9 - Implementing Mass Storage

1. Understanding Partitioning

I've just installed this beautiful NVMe M2 drive into my system, and I can bring it up in my system setup and I can see it just fine. The problem is, it may be great for my computer, but this drive is in no condition to work with my operating system. In order for it to work with my operating system, I have to take this physical electronic device and turn it into a logical electronic device that makes sense to the operating system. If you think about this for a minute, this could be an issue. Number one, electronically, your system sees this particular storage device as nothing but a huge string of LBA blocks going from zero to probably 24 million on this particular one. But when we look at our hard drives from an operating system standpoint, we see files and we see folders, and we want to be able to organise all this stuff using the analogy of a house. If my hard drive is a house, partitioning is building the rooms so that I can put stuff in them. So if you think about what a house looks like now in a human being's house, we'll have kitchens and bedrooms and garages and stuff like that. But in the hard drive house, we're going to have certain partitions that, for example, are where we actually put the operating system. And if you want to boot into Windows, Windows has to actually be on the hard drive. So we're going to separate aroom just for Windows itself. We could also create a swap file room. Now in the Windows world, we actually use files, but in Linux, they actually create a special partition called the swap partition so that we can use virtual memory. Also, what if the operating system partition dies and gets destroyed? Well, it would be nice to have a backup copy. So a lot of hard drives create what's known as a recovery partition, which allows us to bring the operating system back online. And the third thing is, is personal choice. For example, with my hard drive house, I separate all of my large games, which take up gigabytes of data, into their own partition so they don't interfere with all of my office stuff and such. So the idea behind partitions is great, but where do they come from? Well, it's the operating systems themselves that make these partitions. So what will take place is a two-step process. First, your operating system—Linux, Mac OS, Windows—has some kind of tool, some kind of utility that allows you to create these partitions, and then we go through a process of mounting these partitions. Now mounting the partition means that you, as the user at the keyboard, can actually see this partition. How these partitions manifest depends on the operating system. In the Windows world, it's actually pretty straightforward. Each partition is manifested by a drive letter with a colon. So you'll have one hard drive couldbe just one big c colon. Or another hard drive can be c colon, D colon,or it could be c colon, D colon, E colon. It's really, really fun and complicated. We've got lots of episodes that cover it. If we're going to use things like macOS or Linux because they're very, very similar, these different partitions will manifest as a directory tree. So it could be just a little slash or a slash CD Rom or a slash second drive, or it really depends on the operating system itself. But they can manifest themselves in a lot of different ways. So if you're going to be using mass storage, you are going to be partitioning. We use the operating systems to create these partitions, and then once those partitions are created, we can go ahead and access them using whatever nomenclature is right for your OS.

2. MBR Partitioning

If you've got an operating system stored on your hard drive, there has to be a way, when your computer fires up in the morning, that it gets to that operating system, so the operating system can take control. And that's where our first type of partitioning comes into play. This is known as the Master Boot Record, or MBR. It's the oldest type of partitioning out there, and even though it's over 30 years old, you'll still see it sometimes out in the real world. Now, the cool part about MBR is that not only does it define partitions, but it also tells the computer where to find the operating system. So it's kind of like imagining a place where you suddenly say, "Look, just drop the needle right here and whatever is playing, play it." And that's kind of like how the old MBR worked. So in order to do that, there has to be a very specific place where all this happens. And it occurs at a very specific location on all mass storage known as LBA Zero. Let's take a look at this using a traditional hard disc drive. If we take a look at a traditional hard disc drive, we know it's a platter. It could be more than one platter. But for this example, we're going to say it's just one platter. Now, I want to zoom in really close. And if we had a magnetic-reader kind of camera We would actually see that there is one little tiny sector that is known as the LBA Zero sector. which is your computer. assuming this is the first storage device in the boot order. It will automatically start reading whatever is stored here and stored on LBA Zero, which in the old days was something called the Master Boot Record. Or MBR. Now, if we take a look at this, we're going to see that the MBR is broken up into five distinct pieces. First of all, we're going to have a little, tiny area known as the bootloader. The bootloader was the first code read off of mass storage. Your partition tables were now located next to the boot loader. In the old MBR, you could have up to a whopping four different partitions. Now, what's interesting is that, back in the old days, the idea wasn't to give you things like C drives, D drives, E drives, and F drives. The original idea behind this was so that you could run Unix on one, CPM on one, and DOS on one. These are the operating systems of your forefathers. Don't worry about that. But the idea was that you could boot multiple operating systems. So the only real job of the bootloader is topoint to the beginning of one of these partitions. The only thing that would take place is that the bootloader would have to be reassigned what is known as an "active partition." So if you wanted to boot off of this, you would have to have this partition assigned as the active partition. If you wanted to boot off from here, This would have to be assigned as the active partition, and that would be locked into the boot loaders as to which one it would go for. NBR served us for a long, long time, and it's still out there. I know I use past tense because there's something cooler called GPT, but the bottom line is that it worked really well. When it was originally designed, it had a maximum size of two terabytes per partition. Now, that sounds kind of small. Today I've got a bunch of hard drives here. There are four and six terabytes. But 35 years ago, that number was crazy. You're never going to get there. So it was a perfectly fine limitation. Today, it's a big deal. The other issue with MBR is that you can only have four partitions. And back in the old days, like in my Windows system, if I had one hard drive, I would make it one big C partition. wasn't that big of a deal. Today, even in a Windows system, I'm going to have Windows have its own little boot area. Windows is going to have a recovery partition. Windows can have other features. So that limit of four becomes a big problem really, really quick. So what I want to do now is go ahead and take a look at MBR partitions. We're going to be doing this in a Windows environment, but it would be true for any OS. So here we are in Windows Seven. Most of the modern versions of Windows, and especially Windows Ten, don't really do MBR very well anymore, so we have to use an older version. So let's go ahead and, first of all, to see our hard drives, we use a tool called Dismanagement in Windows. Disk management came out a long time ago in a very old version of Windows, and we still use disc management to this day. So what's actually interesting here is, as you can see, it's saying, "I see an extra hard drive." I have two drives in here, one that's running Windows and another hard drive. Like, I just plugged it in, and it's asking me, "Do I want to set it up as a master boot record, or set it up as this thing called GPT, which we'll do in another episode?" So what I'm going to do is set it up as a master boot record. And now you can actually see that I have a disc ready to go that's configured as a master boot record. In fact, if I wanted to, I could convert it to something called GPT, which we will do in another episode. So remember, the most partitions wecan have are four partitions. So in order to create a partition, I need to go in here. We just right-click, and we create—they call it a simple volume. Now, we could say partition just as easily, but volume works just as well. Now it's going to say, "How big of one do you want?" In this case, it's going to say,you've got about 100 megabyte drive. Do you want to make the whole thing one big drive letter?And in this case, I'm going to just say yes. Next, it's going to need a letter for it to attach to. In the Windows world, we use letters of the alphabet. So I'm going to go ahead and just let it use e, and then we have to go through formatting. Formatting is kind of like putting furniture in the room, and we'll save that for another episode. So it's going to go through a process, and it's going to get organized. And what's happened here is Windows has gone ahead and updated the partition table for this particular guy, and now he shows up as one big E drive. And I can go into file management—anything I want. Let's go here. Oops, I can go into file management. I can open it up. And it's completely empty right now because I just made it. But I've gone through the process of partitioning and formatting a particular drive. Now, if I want to, I can just go ahead and delete all this, and we can make it more complicated if we want. Let's say I like to have two partitions in here, so I'm going to go ahead and create a new volume. And this time, instead of just accepting that I'm going to take about half of it, which is about 50,000, I don't have to be exact here. We'll go ahead and call it that if we want to go through this formatting thing. And now we've made half of this physical drive a partition called e, and I can come in here and make the other one another partition. Windows wants to call it F. We'll let them call it that, and we've now made two more partitions. We can actually see all these, if you want, so we can see that the drive is currently empty, but if we look at the computer itself, we can see all of these new partitions. We've taken one physical hard drive and turned it into two separate partitions. Now, the old limitation with Master Boot Record was that I couldn't have more than four partitions. So what they did is they came up with the idea of what we call "extended partitions." Now, in Windows 7, they call them volumes. But I want you to watch very closely. I'm going to go ahead and set up four partitions on this drive, but I want you to watch the fourth one. So give me a second. I'm going to put this together real quick. We've got a total of three volumes created.These are not exactly to scale. If you look carefully, I've got different sizes on them. So I've got a fourth one I can make. Now watch what happens when I do this. So it's 16GB. I'm going to make this 8000 megabytes and give it a drive letter. You'll see how the colour has changed. What you're looking at here is a limitation of MBR. MBR is limited to four partitions. So those partitions are what we call primary partitions. However, you can skip one of those primary partitions and then create what's known as an extended partition. After that, you can add your ReadyLogic drive letters to the extended partition. Now, Microsoft's hiding this from you through terminology, but through the colour of the graphics, we know exactly what's taking place. The green outline you're seeing there—that is the extended partition. Each of these volumes within that green area are known as "logical drives" or "logical partitions." And I'm going to go ahead and make this guy fill the rest of the space. And now we have five partitions on a hard drive using a partitioning scheme where you're really only allowed to have four, right? Well, this is where we get into the whole primary partitions and extended partitions thing. Now, in the Windows world, it looks pretty easy. We just keep making volumes, and it kind of automatically helps us. But with other operating systems, in particular Linux, there are a lot more persnickety issues with this stuff. And for example, after making three primary partitions, we would be forced to make an extended partition if we wanted to keep making more and more partitions on a single drive. Now, keep in mind that when we talk about these partitions, they're per drive. So I could have 17 hard drives in this system, and each one of them could have four partitions. So there's a point where we actually start running out of drive letters, but it's only on a per-drive basis. So NPR had one big benefit, and that was that it worked. And for many decades, MBR was the driving influence on how we partitioned hard drives. Every operating system has a tool that knows how to deal with MBR. But after a while, a couple of things happened. Number one, hard drives got a lot bigger, and that two terabyte limit became a real problem. And also, there were some other situations where sometimes people wanted lots and lots of partitions, and that required a whole new generation of partitioning known as GPT.

3. GPT Partitioning

Many years ago, we recognised that traditional master boot record-type partitioning was going to be insufficient for upcoming storage. And we came up with a new version called GPT, or Guid Partition Table. The GUI Partition Table is designed to take advantage of the power of UEFI biases. In particular, GPT works closely with UEFI to provide you a broad cross-section of extra features. Now, in this episode, I just want to introduce you to GPT, but as we go through mass storage more and more, we'll see advantages to GPT beyond what I described right here. So how's that for a teaser? Anyway, let's cover the basics. GPT has the idea of a guide Guid is an abbreviation for Global Unique Identifier, and it is a 128-bit unique value that defines your partitioning system and makes you unique around the world. If you set up a partition with GPT, it gets a 128-bit identifier that nobody else gets. So it has advantages in security and all kinds of other fun stuff as well. Now, GPT has some huge advantages over MBR. Number one, you can have up to 128 partitions on a single drive. And unlike MBR, there's no primary, extended, or logical; they're just partitions. So we use the word "volume" a lot when we're talking about GPT. Each partition can be the equivalent of 18 million 8-terabyte hard drives. So it's probably going to be enough to cover us for a while. I wonder. Back in the late 1970s, when they were inventing MBR and they heard that they were going to get up to two terabytes, they thought the same thing. Well, anyway, so GPT is a beautiful egg. Number one, in Windows, especially if you're running Windows Ten, you will be using GPT. It's not even really an option to go back to MBR. You can plug in an old MBR driveand read it, but that's about it. GPT is pretty cool, but it also has to be backwardly compatible with MBR. Let me show you how this works. Everything starts with LBA. Zero. Now, the one difference is that there's always a chance that this drive might be yanked out of a GPT-capable system and put into an MBR system. So what we do is we create what's known as a "protective MBR." The whole idea behind a protective MBR is that if somebody with an older system plugs this into their computer, they'll get a little system that says, "Don't touch this computer." It won't be able to read the LBA partitions, but it'll get some kind of little warning so they won't just instantly erase it. Now, the other thing that will be in the protective MBR is that if it's a GPT-capable system, there will be a little piece of information that's part of the protective MBR that says I'm a GPT. So that way, a GPT-capable system will simply go there and go, "Ah, I'm a GPT." It's going to ignore this part and go to the actual partitions themselves. So what's interesting is that we then have to go to the next LBA one, and this is what we call the primary GPT header. And this is going to be storing the information that we need for the partitions. Keep in mind, there's no limit of partitions here and hecan keep taking more LBAS as necessary up to like 128worth, so that it can keep track of lots and lotsand lots of different partitions on a particular system. The last thing that he has that's absolutely cool is that you will have a secondary GPT header somewhere on the system, usually after the primary, and the secondary is just a copy of the primary GPT header. GPT drives are kind of self-healing. If any of this gets corrupted, the secondary can simply take over for the primary and, if necessary, can rebuild all of the partitions. And it really adds an extra level of protection that you've never had with MBR. All this stuff in GPT is really cool, but it's actually anticlimactic because it's all automatic. You might want to be able to configure it to GPT. And we use the same tools we use with NBR. We just get extra features. So let's go ahead and set up a GPT drive. What I want to do now is let's go ahead and go into Windows Eight One, mainly because I'm feeling nostalgic and GPT works exactly the same in Eight One as it does in Windows Ten, and I've fired up disc management. So let's see what's about to happen. I've installed a second drive into this system. Dismanagement says, Hey, I see another drive. Do you want me to set it up as MBR or GPT? We could still use MBR in Windows 8. So I'm going to say, okay. And what we've just done is set up—let me open this up so you can see it, and we can see that we have set this drive up. We right-click on here, and we could actually convert it back to an MBR disk. Do not attempt this in Windows. Ten. So because it says "convert to MBR," we know that it's GPT. The nice part here is that, really, as we make volumes, if you're watching previous episodes, it works pretty much the same way as with MBR. And I've got this new volume e.If I want to, I can easily just delete the volume, and this time I'm going to make some volumes, except this time I'm going to make it three volumes of roughly the same size. So it's 40 GB, so divided by three, it's about 13. We'll make another one here, and you'll see how Windows goes ahead and progresses. The drive letters are for me, and this one, whatever's left over, I'm just going to accept it. And I've got three new drive letters associated with my Windows system. The nice thing is that I could make as many as I wanted and they'd all be simple volumes, so no more extended stuff. And each of these volumes could be 18 8 million terabytes in size. So hopefully this is going to hold us for a good, long time as we progress into the future. The big thing to remember is, number one, if you have an MBR drive, you can convert it to a GPT. All operating systems have this ability. Here in Windows, we do it through Dismanagement, which is probably where the testes are going to be concentrating. Also, keep in mind that when you're dealing with this—starting with Windows 10 and not at the very beginning—there were a couple of revisions of Windows 10. You are now in a situation where you must use GPT. The days of MBR are over, and the only time you're going to be seeing it is with an older system.

4. Understanding File Systems

Partitioning. A hard drive is critical, but we can't actually use those partitions until we go through a final step called formatting. Now, if a hard drive is like a house and partitioning is like rooms, then formatting is like creating nice little shelves so that we can put our folders and our files in an organised fashion within the room itself. So if you want to use a drive, you will partition it, and then you will format it. There's no way around that process. Now, there are lots of file formats out there. You've probably heard of terms like maybe NTFS or HFS, or if you're a Linux person, ext4. All of these different types of file formats tend, for one, to be exclusive to particular operating systems. For example, if you're going to be running a Windows system, you're almost certainly going to be using a file system called NTFS. If you're using a Mac OS, you're almost certainly going to be using a file system called HFS, and we're going to go through all those. But number one, you will tend to use a particular file system with a particular operating system, although there's probably a little bit of overlap. Each one of these different file systems has different features that make them attractive in one way or another. And the exam is going to hit you really hard, knowing these different file systems and what they do. But before we get into that, let's talk generally about what a file system is. Now we know from other episodes that when you create partitions, it sets up these partition tables. We're now going to go through a formatting process and add something else called a file allocation table. A file allocation table is like an index card at the beginning of every partition that keeps track on an LBA-by-LBA basis where all your stuff is on that partition. Let me show you how that works. I've got myself an SSD drive, and I've gone ahead and partitioned it into two separate volumes, which I'm calling C and D. Now, within each one of these, it doesn't actually matter where this is, but there's going to be a data structure called a file allocation table. The goal of this file allocation table is to allow us to keep track of where all our folders and files are located with the "granddaddy" of file allocation tables known as Fat 16. The reason it's called Fat 16 is that it looks like a two-column spreadsheet, and on the left side are going to be the LBA values for every block on that drive. So this is all in Hex. So it goes on and on. Remember, one hexadecimal character represents four binary characters. So it's going to go from zero, zero, zero, all the way down to FF F. Now obviously, this is going to be a pretty big table, so let me just cut this in half because you can't see it all at any given time. So it goes all the way from four zeros to four F's. Now, next to each one of these, you'll find the content of that particular LBA value. And we're going to just zero it all out at first, which means there's nothing there. When you buy mass storage devices, they probably have little bad spots. This was a bigger problem with hard disc drives than with the SSDs that we use today, but it can happen with SSDs as well. So when you get ready to set up this card catalog, one of the things that this format process has to do is go through and query each one of these LBA blocks to make sure that it can read and write data in case errors and bad spots happen. We were going to put orange cones around it, saying that that's a bad block. So part of the format process is to actually go through and check all of these. So it's going to run through literally every block. And the bigger the hard drive you have and the bigger the partitions you have, the longer the format takes because it's checking for you. The result of this is that it can't fix any blocks, but it can put an orange cone around that block. Let me show you how that happens. So it goes through and checks each block. If it finds a bad block, it's going to replace those zeros with a hexadecimal value. That hexadecimal value means this is a bad block. Never, ever, ever use that particular block. And that's just the way we put orange cones on stuff. Now, once all the bad blocks are marked, this particular partition is now formatted in the file allocation table. And by the way, all file formats have a file allocation table. They might call it different things, but there's always some big index catalogue in there that keeps track of this stuff. So once this is set up, we can begin storing files and folders. So what I want to do is take this scenario and go ahead and save a file in this situation. I've taken a little liberty here. First of all, you notice that there are going to be eight hexadecimal characters on the left instead of just four. That's because this is a 32-bit file allocation table. And this is one of the questions on the exam called Fat 32. But it still works the same way. As you can see in this particular example, I've got one and a half bad blocks here and there. So what I'm going to do is save a file called Mom.TXT. So it's going to start right here. You see, this is all zeros. So what we're going to do is we're going to start writing a file called mom.txt. Now, each one of these LBA values stores about 4000 bytes of data. And this is a big, long letter to my mom. and it's going to take about two and a half blocks to store the whole thing. So this is the first available block. You see, it's all zeros right now. So what I'm going to do is start writing into this particular block, whatever that value is. Now the problem is I've got it completely filled up, so I need another block. So what I'm going to do is look for the next available block, which is right below it. And before I start writing on this second block, I'm going to go ahead and write the value of the second block up here. So this is letting me know that we're going to use this block and then this block. So we begin to fill this one up. Now, as we fill this one up, you'll notice it still says all zeros, but we're going to need another block because this is a big letter to my mom. So it's going to jump down to the next available one. Unfortunately, this one is marked as bad, so we're just going to skip over that. And here's the next available block. So before we start writing into this third block, we'll go ahead and write the third block's value here and begin filling this. And now we're going ahead. We don't even use all this block, but the smallest atom of storage space on most hard drives today is 4096 bytes. We lose some space. So let's say we only fill it up halfway. It doesn't matter, we're done. And we go ahead and put four FS in there to let us know that this is called the "end of file." Whenever you're working with these file allocation tables, you'll notice we're not really storing any data in the file allocation table. We're just letting people know where the data is stored. So once we go ahead and write that file somewhere else within the file allocation table, we have either a folder name or something like that. And we go ahead into that folder name and write the name of the file and its size in bytes, its date, and whatever else depends on the file system. and now it's stored. Everything's fantastic. However, a couple of things get a little bit interesting here. So the first thing I want to do is go ahead and write another file onto this file allocation table. So I've got this file called Importantdocument 31.docx that I'd like to save. So, just like with mom TXT, we're looking for all zeros here and start writing it. This is the first available open block, and we begin to write it here. We always put the, we have to go to the next one, right, the second value of the block hereto show that we've filled that one. We keep going. We need more. This is a bad block. So we go down to here, we write its value in here, and we need a little bit more. So we find the next available block, which is right here. can't use that one. That one's also bad. We come down here, and we write it in. And then we put in an F there to show that it's closed. In fact, this is so much fun. Let's do it one more time. And I'm going to add in one more file using the same methodology. So this time we'll use System Storage Docx, and we'll see that it fills in a few spots there. So I've got three files stored on my file allocation table. Now keep in mind that I am skipping that last step. And that is where we actually go once you've written the file. You go ahead and you go to wherever your directory structure is, which manifests itself here just as well. And you would write in things like the name of the file, the date and the time, the bite size, and stuff like that. Okay, here's where the problem comes into play. What I'm going to do now is erase a file, and we're going to run into something called fragmentation. Let me show you. So I've got these three files stored on my system. So let's say, after a while, Important Document 31. Well, you know what, it's not so important anymore. So what I'm going to do is I'm goingto actually put a value this doesn't get changed. Interestingly enough, in the file allocation table over in the directory, I changed the first letter where I save the file name to a lowercase s. The sigma looks like this. And what I'm saying now is that theseblocks are available to be written over becauseI have, quote unquote, erased the drive. So keep that in mind whenever you think you've actually deleted something on a hard drive. You really haven't. So anyway, let's go ahead and add one more file on this. and I'm going to call it Fred TXT. So what I'm going to be doing now is starting to look for available open blocks. Remember, this file has been erased. Now, on some operating systems, what they'll do is protect this in something called a recycle bin. We're going to pretend that's not happening right now. So we're just going to say that all of these blocks, which used to be important Document 31is, we're going to start overriding it.So here we go. We're going to start overriding. This is a big file, so it's going to take lots and lots of blocks. and we go over this. We get to skip over System Storage and continue writing. Now as we put all this in, it probably keeps going from there. You'll notice if you take a close look that Fred TXT is now in two separate spaces on the file allocation table. From an electronic standpoint, there's nothing wrong with this. We call this fragmentation. The disadvantage of fragmentation is that, particularly with hard disc drives that have physical platters for it to scoop up that file, it will have to goall over the hard drive to get it. So we're going to run into this issue more and more. It's not so bad on SSDs, but on hard disc drives, it's a problem. Keep fragmentation in mind as we move forward. OK, so what I've done in this episode is give you a rough idea of how file systems work. So we've had a good look at a file allocation table, and we have some idea of some of the issues that we're going to run into going forward. So keep these in mind, because you're going to see them on the exam.