Storage Adapter Troubleshooting
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Video Transcription
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>> Hey there, Cybrarians,
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and welcome back to the Linux+ course here at Cybrary.
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I'm your instructor, Rob Gills.
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In today's lesson, we're going to
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cover storage adapter troubleshooting.
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Upon completion of this lesson,
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you're going to be able to understand the types of
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storage adapter issues that you
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may see and need to troubleshoot.
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We're going to see how we can locate
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files and use commands to
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troubleshoot storage adapters in
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our demo at the end of this lesson.
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Storage adapter issues are often
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related to missing or out of date drivers
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or firmware and we may also see
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some less common failed hardware issues come up.
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But just like we saw with missing devices,
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Linux looks at an adapter through the lens of
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a kernel module and
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that module is what is used to access the device.
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If the kernel module is missing or not loaded,
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the device isn't going to function.
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We can run lspci-v to see
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the kernel modules that are associated with most devices.
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In this lesson we're going to look at
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information on the common types of storage adapters,
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such as SCSI, RAID and SATA.
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Then we're also going to talk about host bus adapters,
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which can connect various
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different types of storage as well.
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Let's take a look at all of this with some demo time.
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Here we are over in
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our CentOS environment and right off the bat today,
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let's take a look at SCSI.
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We can troubleshoot the SCSI adapter by
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searching for driver and module info.
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The first place to start with this is with dmessage.
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We can run dmessage and then we can grep for sd.
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Here we'll see, for example,
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this line right here,
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sda, attached disk.
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Now in this system, I know that most of
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my actual physical drives are running off of sda.
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That is the device that we're running
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all the storage of for the most part.
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We can see the SCSI drivers that
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are available by looking in the sys file system.
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Let's clear the screen we hit Control L,
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and what we could do is we can do ls/sys/bus
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because this is the SCSI bus.
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We're going to look at SCSI and then drivers.
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When we hit Enter, we'll see that we have
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two different drivers and that makes sense,
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our device is sda,
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we have an SD driver.
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Next we could use udevadm,
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and this is used to get information on
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the driver that's used for this particular device.
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For instance, we could use
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udevadm and we can go with info-an,
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and we're going to get information on
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that dev sda device.
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What we'll do is we'll grep for drivers.
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I'm going to do this case insensitive.
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That's what the i flag is for,
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so grep i for drivers,
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and then I'm actually going to grep for sd.
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In here we can see that this driver,
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the sd driver, is in use on this particular device.
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Now, we can search to see if the sd module is in fact
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loaded on this system as well to make sure
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that we don't have a module issue.
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We could use the lsmod command to do that.
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This returns a bunch of information though.
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What we're going to want to do is
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grep for sd, for example.
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Now we can see that that SD mod is return.
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We can see that the module is loaded.
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We can get some more information about
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this module if you want to you by running
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modinfo and then specifying we want the information
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about sd mod and that will return a bunch of information.
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That is if you spell modinfo correctly, and there we go.
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[LAUGHTER] Now we see a bunch of information.
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Now if we don't see
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this sd module loaded with lsmod, it's okay.
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It might actually be built into the kernel.
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The way that we can see things built into the kernel,
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I'm going to go ahead and clear the screen
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here by typing clear.
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What we can do is we can cut out a file that is
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the lib modules file and what we're going
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to do is we're going to specify the current uname.
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We're going to use uname-r to
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specify the current kernel version.
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I'm just using a sub-shell
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so that I don't actually have to look up
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and type out that kernel from uname-r.
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I'm just telling uname-r to
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put that information right here in my path,
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and then we're looking for the file modules.builtin.
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Now if we hit Enter we can see all of the kernel modules,
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all of the drivers, the modules
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that are built into the kernel.
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If we were wondering if SD modules are built-in,
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we could do a grep for sd.
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We don't see anything here so
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that means that on this system,
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this is a module that gets loaded,
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it's not a built-in module.
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There are, however, other modules
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that are built-in for SCSI.
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If we go back here, let me clear
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the screen and then just type SCSI.
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We're going to grep for SCSI instead and we do see that
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there are SCSI modules that are built into the kernel,
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we just don't happen to have that
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SD module as one of them.
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Let's move on next to looking at SATA devices.
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When we're looking at SATA adapters,
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the first place we want to look at is
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in the PCI list output.
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We can do that with lspci-v,
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and then we see down here at the bottom.
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We can see the SATA controller right
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here and we also see down at the bottom
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that the kernel driver and kernel module in use is ahci.
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As before, we can check to see if this module is loaded.
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We could do an lsmod and then in
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here we can do a grep for ahci.
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We can see that it is loaded right here, ahci.
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Now, next, maybe we want
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to see a little bit more information about that.
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Let's go and clear the screen,
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and I'm going to type clear,
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and then what I can do is I can run
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that modinfo command
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>> to get more information about ahci.
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>> There's all the lovely information about ahci.
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Lastly, if this doesn't come up,
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we can check, again,
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in our lib modules directory here,
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so lib modules uname-r modules builtin.
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But instead of grepping for scsi I'll grep
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for ahci. This returns nothing.
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Once again, this is a module that gets loaded,
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it's not built into the kernel in this case.
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Lastly, if you have
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a SATA device and the disk supports it,
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you can run smart CTL commands to check out
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the health of the drive hardware as well.
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That's something you may want to do
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as well on a SATA device.
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Next, let's take a look at RAID.
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Linux systems can use both hardware and software RAID.
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Software RAID is going to be implemented through
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the multiple devices or MD driver.
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We can review the status of software RAID by
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looking at the file proc mdstat,
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we can do that by doing less on proc mdstat.
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In this case we have no used devices,
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we have no personality, so this is empty.
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I don't have a RAID configuration here,
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so we won't see anything.
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Now, one thing to mention is we just talked about
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the AHCI drivers and when we're working with RAID,
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particularly SATA RAID,
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AHCI drivers are preferred.
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That's because this module or
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driver supports what's called haploid,
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which means that if a drive goes offline in
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a RAID array it won't halt the entire array.
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You can pull that and replace it and rebuild.
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Now, hardware-based arrays are
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a little bit different and they're
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managed with a physical adapter
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connected to the Linux system,
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generally running as a SCSI controller,
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but these are usually connected through the PCI bus.
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In order to look at that, lets
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hit quit and get out of here
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and what we could do is we can run lspci, again,
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list all the PCI devices,
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and now we can do a grep for RAID and I'm
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going to do is case insensitive just in
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case it's a raid lowercase and hit Enter.
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In this case we don't have
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a hardware RAID controller here,
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so we don't see anything, there's nothing on there.
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But that's how we'd go about trying to find
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that information and then go
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from there to start troubleshooting.
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Now the last thing we'll talk about
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today is the concept of
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the host bus adapter or HBA.
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HBA is a hardware device
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that is used to attach a number
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of different devices through a system.
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HBAs could be a circuit board connected to a PCI or
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PCIe or it could be
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an integrated circuit adapter that's
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built into the disk drive itself.
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But HBAs are commonly used to attach
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storage devices such as
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Fibre Channel or serial attached SCSI,
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which is also known as SAS.
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Now I don't have serial attached SCSI
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or Fibre Channel on this virtual machine.
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This is just a virtual machine.
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But if you're going to see these devices,
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we would see them just as before by running lspci-v. We
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do lspci-v to get
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verbose output and then we could pipe this,
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we could grep for SCSI or Fibre Channel.
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I'm just going to hit less here,
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and then we can just era through this information
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and look and see if we see SCSI or Fibre Channel.
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Now I don't have a SCSI or Fibre Channel in the system.
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But if there was, we would see
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the hardware adapter listed
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here as something that's connected to that PCI bus.
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Additionally, we can look for
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a loaded module or driver in lsmod.
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We can do an lsmod,
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pardon me, we're going to quit out of that.
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We can run lsmod and then pipe that to less,
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and we could go through this information and we could
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look for SAS or Fibre Channel.
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We could also go back and take a look at
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our built-in kernel modules.
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We could do things, we could grep for SAS
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or we could grep for Fibre Channel or
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fibre or we can just do ls and we
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can just go through here
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and page through all the different kernel modules.
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But in this case, I can tell you
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we don't have them in the system,
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so we won't see anything.
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But with that, we've reached the end of this lesson.
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In this lesson, we covered the types of
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storage adapter issues
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>> that you may need to troubleshoot,
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>> as well as the files to search and commands
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to run to troubleshoot storage adapters.
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Thanks so much for being here
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>> and I look forward to seeing you in the next lesson.
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