A Basic RAID question

I'd be grateful if someone could help, it's probably a really simple answer:

I'm thinking of buying a NAS, which comes with 4 bays, and the usual selection of RAID options.
What I want however is simply for the NAS to host my 4 x 2TB drives, and for these to appear, over ethernet, in my Western Digital Live media player as a single drive. (I assume that this will be the 'JBOD' option).
What happens if one drive fails? Do i lose all of my data, or just the data that happened to be on that one drive?

In this case, is the rest of the data still accessible?

Dont do that. Use RAID5. You'll loose 1 disk of capacity, but you're protected against a single disk failing - you'll probably find a red light will flash or whatever so you know which one to hoik out. If you want a single disk, the only other option is RAID-0. JBOD does what it says on the tin - presents a load of single disks.

Thanks for the response - my intention is to have a complete mirror of my setup elsewhere (off site) and therefore I am less concerned about drive failure.
With RAID 5 therefore I am paying for an extra drive without benefit.

With JBOD, would a computer accessing the NAS see 4 seperate drives (with 4 seperate drive letters)?

As for RAID 0, it is an option, however i have no interest in the speed aspect. Also, my understanding is that in event of a drive failure then you would replace the drive, then copy across all of the data again - quite time consuming with over 6 TB!

JBOD should show all drives seperately, Raid 0 will use all 4x2Tb drives and show as a single 8Tb drive, however if one drive fails the data will be lost, so going for this option you would need a seperate back up!

If the speed of recovering from a disk failure is an issue I agree with b0redom that Raid 5 is a good option because of the parity it offers. I guess it comes down to requiring 8Tb of data across a 4 bay NAS. If you could get away with 6Tb i would go for Raid 5 personally.

jbod joins all the drives together as one in one massive drive but has none of the speed benefits of raid .
remember raid is not about backup it is about redundancy. even though you have an offsite backup i would still recommend using raid 5. for example if one drive fails in a raid 5 you loose speed but no data and your uptime remains so the raid set can still be used until the replacement drive arrives. if the same happens in raid 0 you lose access to the data until the replacement arrives and then you have have to restore the data.

With RAID0 there is a theoretical increase in speed, although in practice you may not notice it - but if one drive fails, al the data is lost. However as the same is true for JBOD, there is no reason not to use RAID 0 if it is available.

RAID 1 is the mirror option - two drives operate in parallel, if one fails, it can be replaced and the data from the mirror pair is replicated across - useful for resilience and minimizing downtime, but you are using two disks to store one disk's worth of data.

RAID 5 gives you the best of both worlds - data resilience with more efficient use of the drives, but you still loose one drives worth of storage.

JBOD is "Just a bunch of Disks" but depending on how they are implemented, they could appear as independent drives (in which case the data on each one is independent) but I think the sense you mean is concatenation (or Big drive or span) when the drives appear as one - a bit like a logical volume in Linux terms or LDM in Windows.

A couple of useful articles

http://en.wikipedia.org/wiki/Non-RAI..._architectures

or here (more info than you may need!)

http://en.wikipedia.org/wiki/Logical_volume_management