When to erase your system

Often times you may run into a tech who suggests to erase your system. This approach to solving problems typically is drastic and assumes that you are prepared to take necessary steps for recovery.

If you are not sure of success, do not do this, and ask a second opinion of another tech to ensure it is absolutely necessary. These assumptions are often present when the suggestion is raised:

1. You have at least two separate backups on two separate sources from the drive to be erased that have been verified to be healthy and working, and all your information is present on each of those backups. Furthermore, before July 22, 2011 most Macs (links to the exception, which is Macs whose firmware was updated to have the capability after being purchased) came with no internet restore of the operating system. If you have an older Mac, don't assume the internet will have restore options. Make sure your media is bootable if you have installation media before doing an erase.
2. If number 1 is not true, look for an alternative solution immediately.
3. Your drive is too full to perform any necessary troubleshooting of your existing problem.

• you may be able to boot off an external drive to perform the same troubleshooting, and that drive may have more capacity. Consider that option first before erasing the machine.

4 Your hardware is malfunctioning.

• Consider using Apple's supplied hardware diagnostics if it is to do with Apple's own hardware first. If it is third party, look on the third party website for updated drivers. If it is an external replaceable item, find an alternative device to verify it is not the peripheral port that is malfunctioning. Peripheral ports may not work until you restart your computer, or worse until you have reset the system management controller.
• Check power cords for signs of damage. Check AC plugged devices are plugged into known working outlets that lamps can get power from. If a lamp can't get power, it is nothing to do with your machine's software. While hardware diagnostics are not always revealing what the problem is, if they find a problem, you can be sure they exist. http://www.binaryfruit.com/ offers a software called DriveDX that does a more in depth diagnostic of media than Disk Utility of hard drives.

• Sierra and older systems can't "see" hard drives formatted by High Sierra and later with the new APFS format. Attaching newer Macs to older Macs by Target Disk Mode, or connecting to a drive externally formatted by a newer system may render an "invisible" drive that is not damaged at all.

• More rare but it has happened in the past is external hard drives connected during a system upgrade have bridges that may have out of date firmware, rendering them invisible after an upgrade. Connecting the drive to an older operating system reveals them to be usable. The secret is of course to discover who made the external storage medium, and find out if they have published a firmware update for use under newer systems.

• NTFS drives don't have built-in write support on Macs. Macfuse solves this problem.

5 You think your computer is infected. Get your machine inspected by a tech who is willing to diagnose and find all root causes of infection first before indiscriminately wiping your computer. It is very rare that an infection will make a computer completely unusable. One thing that you can use to find out if there are malware installed is get your machine evaluated by Etrecheck. Many contributors to these communities can use the generated report to help you isolate the root causes of your technical issue.