Storage Repair (Demo)
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Video Transcription
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>> Hey, Cybrarians. Welcome back to
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the Linux Plus course here at Cybrary.
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I'm your instructor, Rob Goelz.
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In today's lesson, we're going to be
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talking about storage repair.
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Upon completion of this lesson,
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you're going to be able to understand how
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failing disk hardware can be identified,
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as well as use the storage repair tools such as fsck,
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smartctl, and partprobe.
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Recall what we've discussed previously.
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We said that there's just a handful
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of issues that we might have
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related to storage and these are
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things like running out of disk space,
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disk latency, or failing hardware.
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We covered the first two, and in this lesson,
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we're going to cover failing hardware,
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as well as filesystem repair.
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Now, if there's a small disk portion
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that's not responding I/O request,
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what happens is the disk controller marks
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that as a bad sector.
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Then the controller firmer
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moves the data from the bad sector
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and it just remaps the sector information
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so that the data stays safe.
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However, if you have multiple
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or accumulating bad sectors,
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that tends to indicate a drive failure.
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Now you can see badblocks or
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sectors with the badblocks command, and
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many drives also provide what is called
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self-monitoring analysis and reporting technology,
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or SMART for short.
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For these types of drives,
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the smartctl utility can
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be used to check on drive health.
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Now, some storage issues are
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not related to hardware failure.
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Occasionally, a filesystem itself is broken,
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maybe it has errors or
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corruption, and so in these situations,
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a filesystem check is
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needed and so we use the filesystem check tool,
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which is actually abbreviated as fsck.
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This can be used to check filesystems.
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Now e2fsck is actually what's used to
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check the ext2, ext3, ext4.
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dosfsck under the hood is what's checking
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DOS and FAT filesystems and
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reiserfsck is used to check ReiserFS filesystems.
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But keep in mind, the fsck tool is
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>> not one size fits all.
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>> It does not check XFS.
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>> If you need to do any repair or checking on XFS,
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use the xfs_repair tool on these filesystems instead.
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Now if you do need to replace
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a drive or rebuild a partition,
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the partprobe command comes in handy.
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The partprobe command can be
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used when the partition table on disk has changed.
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Because what it does is it lets the system reread
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the partition table without
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requiring you to reboot the entire system.
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Let's take a look at these commands
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>> with some demo time.
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>> Here we are in our demo environment.
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The first thing let's go ahead and do
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is add a disk to the system.
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Now I'm using virtual box,
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so you're going to see a little bit
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of the behind the scenes there,
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but what I'm going to do is I'm going to do an ll on
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dev and we can see all of the different devices.
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Let's actually do a grep for sd
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because I know the disk that I'm
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going to add here is going to show up
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as a new type of sd device.
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We can see that right now we just
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have sda and then we have
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the partitions on this sda device.
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Let's go ahead. I'm going to go up
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here to machine Settings.
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What I'm going to do is go to Storage,
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Controller, and I'm going to add an additional disk.
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I'll just specify this disk right
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here, and then we'll hit "Okay".
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Now that I've added the disk,
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what we need to do is run partprobe.
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Remember, we're changing the partition table
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so we need to run partprobe.
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So we're going to run that and I'll type in
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my password so that I can
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temporarily become root and run this command.
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This is fine. Don't worry about dev/sr0,
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we always get that message all the time.
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Now we do an ll dev in grep sd,
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we also see sdb and sdb1.
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We've seen that that device has been added
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and we already have a partition on it, which is fine.
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Now, let's check the device for bad sectors.
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We can do that badblocks command that we mentioned.
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You do sudo badblocks.
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What we're going to do is, we'll do verbose.
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We're going to check dev sdb1, and then we'll specify
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if there are any bad sectors by sending
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it the badsectors.txt.
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We don't see any errors here.
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This isn't actually a physical device, no worries.
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[LAUGHTER] But if there were
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any bad sectors here, we would see them.
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If we found any bad sectors,
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we could run smartctl against this as well.
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What we can do is we going to run sudo smartctl -a.
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We specify dev sdb
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because that's the actual device itself.
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Now this isn't an actual physical device
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so it does air out and close,
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which we can see down here.
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It says exiting because the SMART port is unavailable,
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device lacks SMART capability.
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Not a physical drive so there is no SMART.
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But before that, we get all information
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>> about the system, the Vbox hard disk,
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>> the serial number, firmware version, the capacity,
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8.58 gigs, sector size; all good information.
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Smartctl is helpful even when you're
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not running it on a physical drive.
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Interesting. Let's also run an fsck on dev sdb1.
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Now the thing about fsck you need
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to remember is that you have
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to make sure that this filesystem is unmounted.
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For our example, we can just run them out command
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and we can actually do a grep for sdb.
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We don't see any results that indicate
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that sdb is mounted anywhere on the system.
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That's fine, we can move forward with this.
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But you're always going to want to check that
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before you run an fsck
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because you can't run a filesystem check
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on a mounted filesystem.
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We're asking to check out the partition once,
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>> so we'll do fsck dev sdb1.
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>> I'm sorry, we need to be root to do this.
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Let's run this as sudo.
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We can see that it's clean.
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We see all the files have been identified,
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all the blocks, there are no issues there.
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Now, as I said, if this were a mounted filesystem,
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we'd have to take it offline first,
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but this is just an example of how
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you can use all of these commands.
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With that, we've reached the end of this lesson.
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In this lesson, we covered how a system
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identifies failing disk hardware.
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Then we saw we could use some of
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the storage repair tools like badblocks,
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smartctl, partprobe,
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and fsck during our demo at the end of the lesson.
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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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