The solitary confinement part is quite harsh, I've never understood how that is supposed to rehabilitate someone.
In France there's early release, parole, etc. so real time he spends behind bars might be as low as two years.
Edit: The WP article is actually a very interesting read, https://en.wikipedia.org/wiki/Libyan_financing_in_the_2007_F...
I would be wary of going through the appeal court. The judges motivation make it quite clear they were _extremely_ lenient and chose to ignore how contradictory a lot of statement were, and the other cases linked to this. If he is convicted for "subordination de temoin" in the related case, it is likely that his sentence would be set to a longer time.
The fact that Sarkozy started the Lybian war was also outside of the scope of the trial, sadly.