Mac: Replacing a Mid 2010 iMac HDD with an SSD
My mid 2010 model iMac has given me a few issues over the years. First it was my HDD dying, luckily I was able to recover most of the data from it. I say most because I've been unable to find some files in my backups (it's important to sudo that copy command as anything that isn't readable by the user who mounted the drive won't be copied). Apple replaced my HDD and everything was fine until I decided to update to Yosemite.
During the update it reset itself then would refuse to continue past the post-installation configuration stage. At this point I thought that I should just bite the bullet and install an SSD, not as a solution to the problem, but as a fresh start. With the assistance of my brother, who has worked for Apple in the past, we installed a 120 GB Samsung 850 EVO SSD. Using a generic SSD bracket we were able to mount it where the previous 3.5 HDD resided rather than removing other components to make space.
To install Yosemite I'd used Disk Maker X to create a USB bootable installer from DMG installs downloaded on my Macbook Pro, but after a failed install my brother pointed out that the DMG downloaded might have been specific to the hardware of the Macbook Pro which could cause a conflict with older hardware. We then tried a network install from the boot prompt which eventually succeeded. I did have an issue after the final reboot where it would just hang at what looked like a rendering issue with the video driver. We fixed this by booting into safe mode to make sure that there wasn't an issue with the video driver (which there wasn't). We changed nothing, rebooted and it successfully logged into a freshly installed Yosemite.
The next problem we faced was that the previous HDD had a temperature sensor. Since there was no data being sent back the fans were operating at max to attempt to cool the system down. We found many different ways to solve this problem online but most involved a bypass which ignored the lack of a temperature sensor. This would be problematic if down the track there was a problem.
I found a 3rd party app promising to solve this problem, it even offered a timed trial to test it out. The result was that it fixed the problem and my fans stopped sounding like a jet engine. That program was HDD Fan Control. I'm not saying that "this is the solution", just one that worked for me. My SSD has been running at ~30-35°C and I haven't had any further problems.