Existing Server Upgrade - Comments Appreciated

[sebjavierw]

Hi

I currently have a HP Microserver with 8TB (4x2TB) of storage. OS is on an SSD.

It is fully and I am having to delete content, which I really don't want to do.

I also have re-installed and started using a desktop PC from a few years ago.
It has the specifications as listed below:

I really need to upgrade and expand my storage solution. I would like to use the desktop PC as the main server for transcoding etc.
I have a few ideas as how to expand my storage.
1) Add HDD's to the desktop PC and use that.
2) Add HDD's and also use the existing MicroServer as well.
3) Buy a storage tower (Addonics Storage Tower IV) to use as well as MicroServer or Desktop PC Storage.

I am personally leaning towards the external storage tower option. However in order to have an efficient and reliable RAID array I need some advice as to how to achieve this.

Storage Tower:
http://www.techbuy.com.au/p/131556/HARD_DRIVE_-_EXTERNAL_STORAGE_TOWERS/Addonics/RTIVHX535.asp

Do I need RAID controllers, expanders etc.
I am not well versed in RAID controllers etc so your advice is welcomed and appreciated.

I would like to have the infrastructure for 15TB. I would not buy all the drives at once, rather buy them intermittently. I don't want to have to change the infrastructure every time I purchase and install a new drive though.
Trust this all makes sense

Thankyou in advance

Motherboard: ASUS P5KPL
CPU: Intel Core 2 Duo E4600 2.40GHz
2GB RAM
250GB HDD for OS