I'm considering buying a 6 TB Western Digital My Book Studio II to put all my media in one place. Since I have several other drives to use as backup, I'm not planning to do RAID configurations.
My question is: does this drive show up as one large 6 TB drive? If so, what happens if one drive dies? Is the other still accessible or is the whole unit dead? Is that the same if you split the drive into two (i.e., make two 3 TB partitions) ... and is it even possible to setup each partition on an individual disk?
You have 2 options - either stripe or mirror them (RAID 0 or 1). You can set either option via the software that comes with the drive (WD Drive Manager). Bear in mind to change from one RAID to another it needs to format so you will lose all data. Hence its best to decide on which to use and stick with it. It uses hardware RAID so you do not need to do anything in OSX/Windows itself - its all done via WD Drive Manager directly.
By striping them you will get the full 6TB available to you (bar the odd bit for formatting etc). This will show as a single drive on your computer.
If one of the drives fails then you will lose all data across both drives since neither drive holds any parity or backup information about the other.
Not a major issue if you have a seperate backup anyway. A disaster if you dont!
By mirroring the drives you will have 3TB of space available to you (bar the odd bit for formatting etc). Your OS will see a single 3TB disk. Again the hardware manages the RAID, so everything you save onto the disk will automatically be saved onto the second disk at the same time.
If a single disk was tofail, the second disk would take over. You will be warned that the RAID volume has degraded, but you will be able to access all your data and continue working as per normal.
In the meantime you contact WD. They send you a new HDD out (which you pay for). You open the unit and insert the new HDD and send back the old (they then refund you in full). The RAID volume will regenerate and you go back to being protected again.
The striped volume will give you full capacity and will, in theory, be faster since data is being written across 2 disks simultaneously. The only downside is losing all data if a single disk fails. If you have seperate backups then this isnt an issue.
The mirrored volume gives half the capacity and has lower performance (whether you really notice is debateable) as it needs to write the same data to 2 seperate disks. But if one disk fails you continue working as normal and do not lose any data.
Personally I would stripe and use another disk to backup regularly, and then store the backup disk away from the original. Which you choose, depends upon your backup regime and your personal requirments in regards to space required etc.
But I agree, if data protection is a concern then joelks's absolutely correct.