Storage Device Buses Overview
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Video Transcription
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>> Hello there, Cybrarians.
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Welcome back to the Linux+ course here at Cybrary.
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I'm your instructor [inaudible].
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In today's lesson, we are going to be
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covering storage device buses.
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Upon completion of today's lesson,
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you are going to be able to understand
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the types of storage buses that are used in
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Linux and explain the differences
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between these different buses.
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But finally, we're going to examine
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device locations to find
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storage devices and use
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the lsblk command in a demo at the end of this lesson.
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There are three different types of
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storage buses that you may want to consider.
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Two of these are actually going to be on the exam.
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Integrated drive electronics or
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IDE devices have a drive controller
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integrated into the drive itself.
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An IDE supports two devices in a chain.
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It's not actually covered on Linux+,
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but you may see these drives are very old drives and
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example of one of them is the
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>> upper picture on the right.
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>> Then the other types of storage buses are
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the Small Computer System Interface, SCSI,
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which is pronounced SCSI,
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and the Serial ATA Attachment bus, which is SATA.
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Now SCSI and SATA are covered on Linux+ exam,
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so we're going to talk a lot more about them here.
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Now, SCSI is a parallel interface used to
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connect devices and SCSI devices
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are connected in a chain,
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either through an internal or external cable.
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The last device on a chain always
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has something called a terminator installed.
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Ultra 320 SCSI is
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the latest SCSI specification that I could
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find and it transfers data at 320 megabytes per second.
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Now, each SCSI device has an ID,
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and the ID determines the priority of the device.
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There's a maximum of 16 devices on a SCSI bus,
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and the host bus adapter always
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>> has the highest priority.
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>> The priority numbering in SCSI is a little weird.
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The highest priority number is seven,
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and then it goes 7, 6, 5, 4,
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3, 2, 1, 0,
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and it goes all the way back up
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>> to 15 and down to eight.
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>> Now SCSI device interfaces are still
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used for hard disk drives and servers,
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it just became SAS,
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which is Serial Attached SCSI.
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Some virtualization uses SCSI interfaces
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for virtual disk, notably, VMware.
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Now, SATA communicates bit by
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bit serial over a dedicated channel.
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It uses a high-speed cable.
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Just like we saw with the USB,
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the Serial ATA speed has
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gotten faster with each and every release.
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It started out as SATA 1 with 150 megabytes per second.
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Now we're as SATA 3,
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which carries 600 megabytes per second.
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We also have eSATA,
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which allows us to connect
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external devices to the system,
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and eSATAp, which allows us to connect
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those external devices and
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provide power through the same cable.
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Most modern hard drives,
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and optical drives, so CD, DVD,
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Blu-ray drives in any system will use SATA.
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Because everything is a file in Linux,
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the Linux kernel creates
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device files in dev and we know this.
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Dev is used by the kernel and applications to
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communicate with the devices and for storage devices.
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This means that it's used for storing
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and retrieving data on these devices.
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Each device on the system has to have an entry in dev,
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just like we see hardware IDs
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and processes have an entry in proc.
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In device files in dev, though,
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they come in a few different flavors.
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There's character device files.
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Those are things like terminals and
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USB devices that transfer data one character at a time.
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For internal we're typing one character at a time,
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same thing with USB.
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Then there are block device files which
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are storage devices that we're used to
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like hard drives and
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those transfer files in blocks of data.
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Now remember this when talking about block storage,
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the lsblk command is the command that you
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use to list block devices on a Linux system.
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The command list all system
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block devices by device and partitions.
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Alternatively, you can see
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the full path in the name column by using
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lsblk-p. Let's have a look at
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these commands and file locations with some demo time.
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Here we are in our demo environment on Ubuntu.
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Let's take a look at all of
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the device files by just running ls dev.
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This shows us character devices such as the tty files,
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but we also see block devices such as sda and sda1.
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We can also see the device files for standard error,
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standard output, and standard in right here.
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What do you think these do? Well, check this out.
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This is cool. We can do echo
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something and put it to dev stdl,
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and then just write something to the screen.
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Really, that's all the echo does.
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Just as with other device files,
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these exists as a way to talk to
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devices via applications in the kernel.
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Here echo is talking to standard out
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the screen via a device file.
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In the dev mapper directory,
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so you do an ls on dev mapper.
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Here we can see virtually mapped block devices.
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There are none here, but if you go back to Module 4,
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if you need a refresher on this.
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Now let's take a look at the lsblk command.
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We can see all the block devices with lsblk.
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We can also see where the devices are mounted,
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but what if we want to know the path
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to the devices themselves?
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Well, we can run lsblk-p,
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and now we can see the path in the name column.
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What if we wanted to see the
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file system that it's actually mounted to?
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Well, we can run lsblk-p and then fs.
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Now we can actually see the mount point for
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all of these block devices.
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There are a few more lsblk options, but in general,
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just always remember the help option
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is usually there when you do
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a -h and you can see
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all of the various options for lsblk.
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But with that, we've reached the end of this lesson.
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In this lesson, we covered
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the different types of storage
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buses that are used in Linux.
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We talked about some differences
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between SATA and this SCSI buses.
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Then we found out how to
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>> examine device locations to find
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>> storage information and use
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the lsblk command to list block devices.
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Thanks so much for being here and I look
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forward to seeing you in the next lesson.
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