[OT] bad disk & MacOS reinstall

[Riccardo Mottola]

Hi all,

I have a slightly off-topic question.

I think the Hard Disk of my older MacBook Pro is failing. The computer 
has long delays sometimes, in random moments. Maybe at login, maybe at 
application startup. I never see error and when activity resumes, 
everything goes fine, including GIT usage, browsing, compilation. No 
"pattern". Disk Utility reports a verified SMART status and Disk First 
Aid says all is OK.

However Console reports:
kernel[0]: disk0s2: I/O error.

about the same time when he delay started. I suppose some kind of issues 
(eg. going out of calibration, head reset...), maybe nothing is 
corrupted yet, but... I suppose the only fix is a disk replacement. I 
wonder why SMART doesn't alert anything, but maybe the detailed status 
should be inspected. Is there a command line utility that can give more 
detail?

My question is your experience in reinstall.

First way would be to able to format, partition and copy all files to an 
external hard disk, swap and reboot. I have done this once 10 years ago 
in PowerPC times and it was not trivial and they sell software to do 
that, which I don't want to buy.

Second way would be to reinstall MacOS 10.11 (no DVD available...) from 
scratch and then copy or reinstall things  (including MacPorts, of course).

With a "new" hard disk, what is the best way to reinstall OS like Apple 
supplied? In the past I had some bad experiences with Internet install 
not working/completing with weird errors.
Also, I'd like to have disk utility and recovery working. I wonder if it 
will work or some magic partition needs to recreated?
Hardware Diagnostic Tools need to be installed extra, I have read.

Riccardo