Troubleshooting Boot Issues - CompTIA A+ 220-1101 – 3.7
Let’s have a look at troubleshooting boot issues.
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Boot Process
Before I look at troubleshooting boot issues, I will first have a quick look at the boot process. Understanding how this works helps when troubleshooting boot problems.
Initially, the power supply sends a 'power good' signal to the CPU, effectively resetting the CPU and other hardware, preparing them for operation. For the computer to start functioning, the CPU needs some code to run.
On the motherboard there is a BIOS or UEFI chip. This contains basic firmware to run the computer. This firmware is transferred to the memory to be run by the CPU.
The CPU now has some code to run. It can be used to access the computer setup to change settings on the computer. The computer can also start the boot process. Essentially the firmware provides a very basic code to run other software. This is enough to start the boot process. So, let’s have a look at what happens next.
Boot Order
The boot sequence of a computer is configured in its system setup, allowing you to specify the order in which different devices are checked for a bootable system. Additionally, most computers offer a hotkey option at startup to specify which device you want to boot from. Pressing this key during the boot process opens a menu where you can choose a specific device to boot from on a one-time basis. This feature adds flexibility to the boot process, allowing for temporary changes without altering the permanent settings in system setup.
When your computer fails to boot, one of the primary checks should be to ensure it is attempting to boot from the correct device. If a storage device malfunctions, the computer's setup may automatically switch to other available storage options, like a second hard disk. It's crucial during troubleshooting to verify that you're focusing on the right device. For instance, if your primary hard disk fails, your computer might try booting from a second hard disk. In such cases, troubleshooting symptoms related to the wrong storage device can lead you astray.
When a computer bypasses its normal boot device and starts booting from or trying to boot from an alternative source lower in the boot order, it often indicates an issue with the primary boot device. Thus, when you see this occur, it is best to start troubleshooting from the storage device the computer is supposed to boot from.
Real World Example
Here is a practical example to illustrate how boot issues can arise. I was once involved in migrating company data from internal RAID storage to a Storage Area Network or SAN. The migration was successful. The server was configured to boot from the SAN rather than the internal RAID. This transition went smoothly, and the server operated well after the change.
After a few days of the server working well, we had a power blackout. The UPS did its job correctly and shut down the equipment and we just had to wait for the power to come back on.
The power came back up and the server started up. However, the server started faster than the SAN did. Thus, the server failed to boot from the SAN and went to the next boot device which was the internal RAID. The server was thus running off the internal RAID which contained data from before the migration.
Unfortunately, we never noticed what had occurred until we got a phone call from a user saying there was something wrong with the data on the server. We quickly shut the server down, disabled it from booting from any other device other than the SAN and started the server up again.
The lesson to be learned here is that, when supporting computers, if you have multiple boot devices, consider disabling ones that you don’t need. Most modern computers will support pressing a key on startup for the rare occasion you want to boot off another device.
Let’s consider what happens when the computer tries to boot from a storage device.
Booting from the Boot Sector
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References
“The Official CompTIA A+ Core Study Guide (Exam 220-1101)” pages 102 to 202
“Picture: BIOS” https://en.wikipedia.org/wiki/BIOS#/m...
“Picture: UEFI” https://en.wikipedia.org/wiki/UEFI#/m...
"License" https://creativecommons.org/licenses/...
Credits
Trainer: Austin Mason https://ITFreeTraining.com
Voice Talent: HP Lewis http://hplewis.com
Quality Assurance: Brett Batson https://www.pbb-proofreading.uk