I have a MacBook Pro 13” Early 2011 which is still running without any problem until now. The RAM had been upgraded to 8GB and the Apple HDD had been replaced with a Corsair Force GS SSD 240GB as the main disk. The SuperDrive was removed and replaced with Apple HDD by using an OptiBay or HDD Caddy. It has been running perfectly for more than 2 years.
As the Apple HDD is only 320GB capacity, its free space is almost running out now so I decided to buy a new 1TB 2.5” Hitachi Internal Hard Disk (Model: HGST HTS541010A9E680) SATA-3 (6.0 Gbps). I installed it in the OptiBay or HDD Caddy to replace the 320GB of Apple HDD.