Q: Wary of El Capitan

In mid-December, I downloaded El Capitan 10.11.2 and installed it on a 70gb partition. Everything seemed to be working well, as far as I could test. I booted into the El Capitan partition several times while comparing it to Yosemite; I never had any issues, but then I had proper work to get on with and had to stop playing with the new OS. I had some time the other day to proceed with the upgrade on my primary partition, so I tried to load my test partition again...it failed to boot.

While it failed to boot, I did not experience my boot failure the way many others described: the system sound would chime, the Apple logo would appear, the progress bar would load...but only about half way, then my machine would just shut down. I had zero issues booting to my primary partition. I tried to reinstall El Capitan onto the test partition, but that failed. I tried to install Yosemite onto the test partition, and that failed, too. I didn't download or install any programmes on the test partition; the only thing I did was open various existing apps to ensure they worked properly in the new OS. Then I didn't touch the partition for weeks, and it spontaneously stopped working.

I wish I had tried to solve the problem first because now I am trying to work backwards. I ended up wiping the partition and removing it. Then I tried to install El Capitan in Parallels, but Parallels could not find or recognise the El Capitan image file. When I opened the Mac App Store to re-download the file, red text was displayed next to the greyed-out download button that said an error occurred. I deleted the old OS install file and downloaded a fresh copy. Parallels still didn't recognise it as an OS. So, I created a new partition and installed El Capitan again. It is working fine, just as it did when I first installed it a month ago. I have restarted, shut down and started, and booted in every possible sequence that I can think of, and it is still working without issue.

However, I am still wary since I don't know what caused the previous errors. Has anyone else had a similar problem? Could the partition have corrupted? I am eager for the El Capitan upgrade, and, even though I have a solid Time Machine backup in place, I don't know if I should risk it yet.