Recently I had a terrible time with my MBP and I couldn’t figure out what was going on. It turned out that a hard disk was failing, this only became apparent after a few weeks of bad experience.
Intermittently there would be severe lags in response to just about any action, no error messages showing anywhere and no signs of any sort of trouble. The timing was bad, to say the least. Eventually, the second disk on my MPB started to eject itself frequently and wouldn’t be visible. I had to reconfigure my machine to have all my files in the single functioning disk. Once this happened, my laptop became the nippy device I was accustomed to.
The early signs: every now and then the laptop experiences long lags, no errors shown. Because this was happening at a time when I was working on an assignment on a different setup. I started blaming everything new I had installed and would reinstall and reconfigure programs hoping that would be the cause, alas to no effect.
Eventually, some clues: the disk would intermittently auto eject. This forced me to find a location for the files I needed in the project I was working on. I run Disk Utility a couple of times and it did show a serious problem with the second hard disk. I had no time to dig into this, chose to wait until my engagement was over.
The final straw: only one disk now available in the system. Once this happened, my MBP started behaving normally again.
I was lucky to have had partitioned off my data such that the boot drive had all the essential programs and files needed to run the computer. The second disk mainly hosts data, and nearly all of it was frequently backed up and copied to a second machine. If I fail to recover the disk, I would only lose a few days of work. The project I was working on, when the incident started to occur, was all based on a GIT repository and I was pushing my changes at the end of the day, so didn’t lose any work there. Thank goodness.