I have a MacBook Pro 17" (Early 2011). It's been working well and the hard disk has not been exhibiting any problems ever. Until now it seems. I upgraded to Sierra (from El Capitan) through the Mac App Store, it downloaded it, restarted to install, but then it says:
"OS X could not be installed on your computer
File system verify or repair failed.
Quit the installer to restart your computer to try again"
However, each time I retry the same thing happens. Someone on another post I found that was similar said to start up using Cmd-r (holding while it restarts) to go to OS X Utilities, and then Disk Utility to repair the disk.
However, when I try to run First Aid on my internal Macintosh drive, it fails. One of the things it says in the log is "The volume Macintosh could not be verified completely", then a few lines below "File system verify or repair failed" then "Operation failed".
So what can I do? I do not have any back up, or an emergency disk or start-up disk. I have never come across a problem like this before.