I have a mid-2010 iMac running High Sierra and I'm taking it to a local shop to get my fusion drive replaced with an SSD. I of course have sensitive info in the Notes App and elsewhere on my computer. What is the best way to ensure the security of my iMac? Is there any way of doing so without deleting everything?
Everything is going to get deleted anyway. Replacing one of the drives in the Fusion pair will render both parts unusable and very difficult to recover data from.
Assuming you've got a backup, which you will use to restore your data onto the new SSD, then you will lose nothing by erasing the Fusion devices.
Normally, the best practice for securing sensitive data is to encrypt the volume, but there's no point in this instance, as it takes time and is quite stressful for an elderly mechanical drive.
You could set up full-disk encryption via FileVault, which will keep your data in-place. You could also wipe the drives using secure erase. I don't know what your shop's procedure is for replacing drives, but I'd recommend making a backup, and if you have anything sensitive on that drive, it's probably in your best interest to encrypt it or wipe it.
This depends on whether the shop will just replace the hardware (so you need to restore from backup afterwards to reinstall the system) or whether they also migrate your data directly.
- If they just replace the hardware, make sure you have a useable backup (or even two to be on the safe side). If your current disks are encrypted with FileVault2 your disks are unreadable without your password, so as long as you pass your password along you don't need to take additional steps. If your current disks aren't encrypted, either enable encryption (and wait for it to run through) or reformat (with the most secure option) from Recovery
- If they replace the hardware and migrate your existing data they will have access to your data while doing so (they even will need your password in case the current drives are encrypted)