[G4] EIDE and Ultra ATA RAID

[Philip J Robar]

On Apr 25, 2005, at 1:42 PM, Ralph Garrett wrote:

> On Apr 25, 2005, at 2:52 PM, Philip J Robar wrote:
>
>> Note that concatenating a bunch of disks to look like a single  
>> disk has the same problem as a stripped array - if one drive fails  
>> you loose the data on all the drives.
>
> I disagree, concatenating drives is similar to striping but not the  
> same. Instead of writing the data to ALL of the drives in the array  
> simultaneously, the data is written to one drive till it's full and  
> then written to the next drive in the array. If a drive fails in a  
> concatenated array, the only data lost is the data on the failed  
> drive and any data that may span across the 2 adjacent drives in  
> the array. Concatenating/Spanning drives is usually done to  
> increase the storage area beyond what single drives can cover and  
> offers no performance boost.

There's no guarantee with spanning (A.K.A. concatenation or JOBD  
(Just a Bunch of Disks)) that you will easily be able to recover data  
from the drives that did not fail. How hard that will be depends on  
the raid hardware/software, the file system used and the OS the disks  
are deployed on.

Phil