This might work for you, but I would be concerned about running a system critical drive on an HDD in a data doubler. If you look around the forums, you will see many people have had problems with using SATA-III (6.0 Gbps drives) in their Optical bays. I would be highly critical about attempting this with a critical configuration such as a RAID0 software volume as your boot drive...
I would recommend that you reconsider your plan here as you are setting yourself up for multiple problems.
Adding the second drive is fine but combining the two drives in a RAID 0 array especially for your root drive is a mistake. First RAID 0, while increasing access speed, doubles the likely hood of a catastrophic drive failure. If either drive fails all tour data is gone not just what was stored on the failing drive.
Second while OS X can be installed on a RAID array it will not create the recovery partition if you are installing Lion or Mountain Lion.
RAID 0 has some limited uses in applications like video editing but even there the rule of thumb is not to store on the RAID 0 or else to be baking up almost continuously.
If I can ask, why are you looking to setup your system this way?
Whoa, thanks for the advice guys! I will reconsider my original plan.
The reason I'm thinking of this is because my HDD is full. As I am a photographer, and take lots of photos, I need to expand. I thought why not RAID 0, but it seems I will just use the second HDD as an Aperure library (my pics take up the most room anyway).
As I am a photographer, and take lots of photos, I need to expand.
Eeek, DO NOT consider any internal HD as storage or expansion, unless youre prepared to lose a LOT of valuable data.
backup and at least 2 archives of your valuable data.
All pros consider a single off-computer copy "not enough". They will at least agree to that much.
One backup, and 2 archives.
At very minimum 2 copies of your data OTHER THAN on the computer itself.
Idealized minimum backup and archive
The best minimum idealized storage of your entire system hub and data hub are 4 autonomous copies.
First that of your system and APPS (and any resident data) as kept on an ever-updating Time Machine backup (preferably also a clone of the entire drive, for faster return in case of HD crash).
Secondly a HD archive of your data hub (vital files).
Third (unless too large in size for same) a copy archive of your data hub as stored onto archival DVD media, or if this data is too large, on a third (or additional hard drives) drive stored safely away in a firebox, safe, or safe deposit box.
(mostly a professional route) Fourth and final is a secure online archive on a private website. Cloud based storage should not be considered for this due to security concerns, and the transient ephemeral nature of cloud storage which can only be quasi-possessed.
Simplex rules to always remember about your important data
Data redundancy (copies) makes all HD crashes inconsequential, an irrelevancy.
Always have a system (OS) hub copy (TM or a clone), and at the very least two copies of your data hub, and preferably a third offsite and securely online.
Compartmentalize your system (OS) hub backup vs. that of your data hub archives, in so doing any failure in your computer (system [OS], data, computer) becomes quick to recover from!
Any Macbook or desktop should be idealized as a working platform computer system, containing all your applications, documents, and weekly-use necessary files; and all media files such as ‘big-data’ (music/PDF collections/video/pictures), unless directly needed in the near future, should be kept off the computer and on external storage USB or likewise bare hard drives.
Never consider any computer a data storage device at any time under any circumstance, rather a data creation, sending, and manipulation device. Anyone who thinks data is safe on any computer, even copied upon multiple partitions is making a mistake that will, without fail, strike.
Never backup your data exclusively upon magnetic hard drives or flash storage, nor consider same since magnetic storage degrades over time, roughly 3-8 years, even under ideal storage conditions.
Store important data on multiple servers on multiple continents. Private website domains are very cheap and yearly hosting costs are often under $100 for unlimited storage.
Burn important data onto multiple copies of professional grade archival DVDs (Taiyo Yuden or likewise) and store them in cool dark fireproof safes, a safety deposit box, or multiple places.
Most importantly know that 2 copies of your data is 1, and 1 is none, and 100 copies stored in one place or building is also the same as none due to fire or natural disasters.
Since SSD are generally small, keeping your internal HD data as trim as possible is a big benefit for several reasons, namely it speeds up the cloning process, makes upgrading from a HD to a SSD a straightforward process by keeping the HD data size equal or less than the size of the SSD upgrade.
Always consider and expect your computer’s hard drive or SSD to completely crash anytime, at all times, and you should keep a cloned and updated hard drive handy of your system hub (OS and APPS) at all times to return to immediate productivity and utterly avoid application and parameter reinstallation and tweaking. Nothing is quicker than taking out a dead HD and installing in a new updated cloned HD for getting back to 100% in under 20 mins; or quicker still attaching the cloned HD to USB and booting from it to return to working condition immediately. This cannot be done with Time Machine.
When your data is decentralized, it becomes both everywhere and nowhere, accessible to yourself (and those whom you choose), destructible by none, cannot be collected together or permanently retrieved under any circumstances. In so doing, worries about data corruption, hijacking, loss, theft, erasure, degradation, and natural disasters or fire has been transcended and becomes a moot concern. Little effort is required to accomplish this, and given cheap costs of data storage, there is no excuse anymore for the loss of vital data.
Ultimately we spend 1000's of hours creating and saving data, however we spend a great deal of time protecting our computers and notebooks, with cases and insurance, accessories and upgrades,...but most give little to no consideration to their data which is the most important. In the thought of what a notebook costs vs. what 1000's of hours of work creating data is worth, the computer itself is worthless by comparison in cost. Therefore much more due prudence is necessitated in the thought towards protecting your data as was spent in concern over the computer itself.
Hard Drive life:
Given the second law of thermodynamics, any and all current mfg. HD will, under perfect storage conditions tend themselves to depolarization and a point will be reached, even if the HD mechanism is perfect, that the ferromagnetic read/write surface of the platter inside the HD will entropy to the point of no return for data extraction.
HD life varies, but barring mechanical failure, 3-8 years typically
Ferromagnetic depolarization due to entropy makes even the best HD money can buy, a Hitachi drive. utterly CORRUPT in 4-6 years average of static storage.