Given a scenario, troubleshoot hard drives and RAID arrays with appropriate tools: CompTIA A+ Exam 220-901 sub-objective 4.2

Back to the main 901 ExamNotes page

Detailed (and official) description of CompTIA A+ sub-objective 4.2:

4.2 Given a scenario, troubleshoot hard drives and RAID arrays with appropriate tools.

Common symptoms
– Read/write failure
– Slow performance
– Loud clicking noise
– Failure to boot
– Drive not recognized
– OS not found
– RAID not found
– RAID stops working
– Proprietary crash screens (BSOD/pin wheel)
– S.M.A.R.T. errors

– Screwdriver
– External enclosures
– File recovery software
– Bootrec
– Diskpart
– Defragmentation tool

Welcome to ExamNotes by CertBlaster! This objective is technically Hardware but as you’ll see it has a software thread running through it. Don’t ever think about these tests in a strictly hardware or software sense. You know we need the software to direct the hardware and the hardware to run the software. With that behind us we’ll move on: Here we are asked to troubleshoot hard drives and RAID configurations with the appropriate tools.

We should start out by examining the devices and configuration you are likely to encounter. First we will look at the drive, then the configuration possibilities and or problems that may occur in the particular configuration.

Hard Disk Drives (HDD)

This is by far the most recognizable component in modern hardware. It has however undergone lots of changes. Since the first HDs to today the principle is the same. You have a sealed enclosure that contains several magnetic platters the read write heads and all the objects that make the operations possible. We’ll look at them closely later. For now a basic hard disk can come in two physical sizes 2.5” and 3.5”. Doesn’t sound like a big difference but it is. The smaller size accommodated the limited space requirements of a portable machine. Also the smaller size reduces the energy requirement saving valuable battery life.

Let’s get started with the original (commercially available) drive. This is the venerable 3.5” magnetic hard drive. This drive has been in use since, believe it or not, one could consider 5 MB a sufficient amount of storage and would serve their foreseeable needs! A decent system would cost in the neighborhood of $3,000.00. And you could get your own copy of the groundbreaking Windows95! The world has not been the same since!  Drive sizes Processor speed and memory were all advancing at the same impressive rate. But, I digress. Here is a great shot of the inner workings of a HDD before we take the crayons to it.

close-up photo of Hard Disk (HD) internal asembly
Hard Disk Drive (HDD) internal asembly

Inside the Hard Drive

Look at the perfection of the platters. That level of quality and integrity is essential to ensure reliable performance and long Mean Time Between Failure (MTBF).This Is a numeric representation of the average useful life of a component usually measured in tens of thousands of hours. If you are responsible for the maintenance of hardware for your company one of the many essential tools is an external hard disk enclosure. This greatly simplifies the process of swapping drives in and out of your machine for testing. Further it allows you to check the cables and connectors involved to validate them.

Here is a 3.5” hard drive, open and labeled. This provides good detail on the components inside the enclosure. We’ll start with the Platters.

graphic showing the internal details labled of a Hard Disk (HD)
Hard Disk (HD) internal details labled

These are very precisely machined and metallically coated platters designed to hold your data in incredibly small sections called sectors. The data is read from and written to these sectors by the heads. There is a head for each platter. The platters are double sided and can hold different data on either side. The tolerances in here are quite tight. Consider that a drive having three platters can easily hold 2TB of data. The heads are controlled by an actuator consisting of very strong rare earth magnets that control the actuator arms that hold the heads, in precisely the right positions and can move rapidly to the next location. Ok, now this is where your speed is generated. You combine the rotational speed of the platters with the ability to read/write efficiently to either side of any platter and you have the speed and efficiency you need. Higher read/write metrics can be achieved by increasing the Spindle speed. Speeds available are from 5400 RPM to 10,000 RPM and above. There are advantages and disadvantages to everything, no exception here. Let’s say you want to get more speed from your laptop by switching to a 10,000 RPM from a 5400 RPM. Your laptop will get faster but your battery will run out twice as fast. So that’s the trade.

Common symptoms

By far the most common complaint about a working machine is slow performance which many users tend to blame on the hard drive. Others blame the processor or memory which is a little closer to home.

Slow performance

Poor hard drive performance can be blamed on a number of conditions and there are solutions for most of them. For a slow drive you will want to use system tools to define and possibly repair the problem. These tools would include Defragmentation. As you see in the illustrations, it is possible for a large file to exist with parts spread all over the disks. Parts of files that are not directly (logically) close to each another are called fragmented, with a fragment here or there. Reading a file that is spread out like this takes longer. The process of defragmentation (Defrag) moves the associated files together in a contiguous arrangement that is easier and faster for the drive to read, and creating clear free space to write data in. The result is faster reads and writes. This is a once a month preventative maintenance activity.

Now we’ll move to problems that are associated by their cause’s or repairs.

Here are some drive errors that can be pinpointed and possibly remedied in UFEI/BIOS.

Drive not recognized

The drive was not auto-detected and the setup data needs to be configured manually. OR the drive has been damaged and cannot be recognized by the system.

OS not found and/or Failure to boot

The drive is improperly set up. OR Drive is damaged beyond repair. The operating system boot files. Are always located on the outermost track of the hard drive the space is reserved for this purpose alone.

RAID not found

This would indicate that the RAID controller has failed or one or more disks is misconfigured.

RAID stops working

This would indicate that one or more of the RAID disks has failed.

Reporting Technology (S.M.A.R.T) this tests critical areas of hard drive functionality quickly during boot to assess drive “health”. S.M.A.R.T. errors appear while there is plenty of time to act, provided you act. It’s not the sort of error that will go away.

Proprietary crash screens (BSOD/pin wheel)

This screen is a death by degrees sort of thing. With a BSOD (Blue Screen of Death) it’s pretty much as the name implies. By the time you see the screen your system is already dumping the contents of memory into a DMP file to be used to diagnose the cause. The pinwheel indicates that the program you are running has crashed and taken some system functions with it. You may be able to use Task Manager to recover.


Here is a look at some of the software tools that can get us out of jams in addition to Defrag.


This command depending on the parameters used can check a drives overall condition all the way down to predicting sector failures and getting the data off of them before there is a problem.


Use format when you are ready to start fresh, because you will be. Formatting a Windows disk essentially clears all data from the disk.

File recovery software

If you have it turned on. Turn it on now. Windows has the system restore feature that will restore your system back to a point before you had a problem. Also Windows SFC (System File Checker) will check critical windows system files and restore them if necessary.


This command can be used to repair the boot sector of a hard drive including the files that belong there like the MBR and BCD.


This is a command line disk partitioning utility. It can be used to delete all partitions on a disk or to re arrange the sizes of partitions provided there is space. Diskpart on a new drive can create a partition, initialize it and format it in preparation for the operating system.

Back to the main 901 ExamNotes page

That’s all for 4.2! Good luck on the test.

Leave a Reply

Your email address will not be published. Required fields are marked *

On Facebook

Trust Guard Security Scanned
Share This
Real Time Web Analytics