Smitbret,
I mentioned RAID cause although the data is not critical I have spent time gathering it so I just wanted to have a way to save the data if one drive fails. I understand that this is not back-up.... my whole point over here is to have a folder which has 3TB to start with and as I add new drives all that space is also available for the said folder.. right now i have two 3TB drives which are empty...
How is JBOD different than RAID and would it be a better option than RAID?
JBOD of drives is like you have 4 pieces of different sized rope:
1 foot
4 feet
2 feet
3 feet
If you tie/splice them all together then you have 10 feet of rope. That's JBOD.
RAID is different and there are different types of RAID. I'll give you the most common examples, but Googling RAID or hitting it up in Wikipedia will be more thorough and probably more accurate.
RAID 0 is where you take 2 or more drives of equal size and spread the files across all of the drives. For example, if you have 3 drives in a RAID 0, the files would be broken up into 3 parts and each drive would have a part of it. Makes accessing data much faster because you can access from all 3 drives at the same time. It's also very risky because if one drive dies, you lose ALL of your data because 1/3 of every file is missing. The more drives you have the more risky it gets because 1 dead drive kills everything. You have to start with empty drives because everything gets erased on all the drives when you set it up. Adrenaline junkies like this type but it is not safe at all.
RAID 1 is where you have 2 (or 4 or 6, etc.) drives set up to mirror each other. You have two 3TB drives but they are mirrors of each other. When you save a file, it saves an exact copy to each drive. If one drive fails, the other takes over. It is quite safe, but won't protect you from things like accidental deletions or if a power surge fries everything in your PC.
RAID 5 is where you have 3 or more drives set up and the data is distributed in a way that allows any 1 drive to fail but you'll still be able to run and recover as long as you don't lose another and you lose the space of one of the drives. For example, you have five 1TB drives in a RAID 5. The space available would actually be 4TB instead of 5TB because of redundancy. It's slower to write because of space calculations but is safer than JBOD or RAID 0 but not as safe as RAID 1.
RAID 6 is like RAID 5 but with 2 drives setup for redundancy and so you could lose any 2 drives and be OK. Five 1TB drives would then give you 3TB of available space.
There are other types like 0+1 and RAID 10 but they aren't common for home use.
These RAID setups can be done either hardware or software, but the end results are usually the same. The difference is that true Hardware RAID doesn't steal CPU cycles to calculate Parity and Redundancy so it is faster than software where your PC's CPU takes care of it.
Then there are the newer versions that aren't technically RAID but follow the same ideas. ZFS is a new file system like FAT32 and NTSC. With ZFS you can set up RAIDz1 or RAIDz2 that are just like RAID 5 and RAID 6 except ZFS brings a lot of tools to the table to protect your data from corruption and bitrot. There are lots of iterations of this like FreeNAS and Solaris and most are free but they run on their own Linux distributions and can be a little limiting if you want to do anything besides just store and serve files. You also have to start with empty drives for this, too.
Then, there are the non-RAID, Parity options like unRAID, FlexRAID and SnapRAID that have their own "versions" of RAID 5 or 6. They are software and generally less expensive to implement than true RAID and ZFS solutions. They are also slower but if you don't need it to handle huge amounts of I/O requests and just want a centralized place to store photos, files, music and to serve up the occasional video to a normal home then they are plenty fast. The advantage of these is that you can continually add drives to them and expand your storage space.
With your limited budget, I would steer you in this direction, particularly towards unRAID.
Take that $200, buy an unRAID license, a 1GB flash drive and a 2nd 3TB HDD. One of your 3TB HDDs will be your parity drive. Every drive after that can be used as a storage space and you can continually add on for as many drives as you can stuff in your PowerEdge and it doesn't matter how big they are. The OS actually runs off the flash drive. No HDD needed.
From the info you've told us, you would then have two 3Tb and a 36GB drive. In an unRAID setup you would then have ~3036GB. Any drives you add to it would just be additional space. You are just limited by the size of your parity drive that has to be the same size as your largest drive. If you wanted to add those externals to the array, just copy their data to the array you've already created, then clear 'em and add 'em in. If you had a couple of 500GB external HDDs then you'd have added another TB of storage and as soon as you rebuild the array it's all parity protected.
So if you wanted to start using 4TB drives then you would slip a new 4TB in as the parity drive and move the 3TB in to hold data. Your storage space would then be ~6036GB and if you added another 4TB you'd be at 10+ TB. Just keep adding drives as you need and your budget allows. You don't have to lose data or erase anything. You just have to clear the drives before you add them to the array.
unRAID also has a Plex plugin so you can stream your media, too. The other nice thing about unRAID is you can pretty much just use any old hardware that you have lying around. It is VERY light on resources, doesn't require much RAM and you would only need to consider CPU speed if Plex is transcoding your video files.
FlexRAID is similar but runs on top of an existing OS like Windows and allows you to import disks that have data on them. You'd also have to install the OS to a HDD. It also has its own version of RAID 6 if 1 parity disk doesn't make you feel safe enough. SnapRAID is very similar to FlexRAID and is open source but uses CLI for administration. There's a GUI for it called Elucidate but I never could get it to work quite right. I'm sure I'm just an idiot.
Sorry for the length, but you don't just either RAID or not. Lots of stuff to look into.