I want to add dual ssd ( two 2.5" ssd)

There are 2 drive bays in this machine. One is for a 3.5" SATA drive, the other is for a blade type PCIe SSD, which has very limited compatibility.

So yes, it is possible, but you'd need to do a bit of a fiddly update, and the PCIe SSD will be very expensive, especially when dealing with larger capacities.

The other issue, is that the 3.5" drive in your machine currently, is used to adjust the internal fans RPM speed. Its SMART disk temperature data is used for this, but it has specific firmware to make it happen, so standard SSD (which come in a 2.5" SATA form factor) will need a separate cable to make it work without causing the 'runaway fan' issue. (basically, the CPU fan will spin at full speed all the time, as it cannot get accurate temperature readings from the drive)

The only option for that, is to use a cable made by OWC to override the sensor data. This is the item i'm referring to:

http://www.thebookyard.com/product.php?c...

So in essence, it is possible, but will be expensive.

You will need the following (not including tools or the replacement VHB display tape kit, which is required every time you cut the display off the body of the machine. see the tear down for these details)

2.5" SATA SSD

2.5" to 3.5" Adapter (Newertech AdaptaDrive is a suggested option)

OWC In Line sensor cable

Larger PCIe SSD Compatible with the range you have

On another note, its worth noting the exact range that you have, as the SSD speeds vary from Late 2014/Early 2015 and the Late 2015 model. So if you have the latest model, you'll want to make the most of the speeds and find a faster SSD for the machine.

(the blade SSD also fits behind the logic board, so it will need removing to fit it. so its a labour intensive job)

I hope this helps.