A Basic RAID question

[MSIC]

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?

[b0redom]

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.

[MSIC]

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!

[chris_argyle]

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.

[alsenior]

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.

[peterb]

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