[G4] EIDE and Ultra ATA RAID

[Alex]

On Apr 25, 2005, at 19:40, Ralph Garrett wrote:

> On Apr 25, 2005, at 5:51 PM, Philip J Robar wrote:
>
>> This is simply not true. Every drive you add increases the chance of 
>> the array failing.
>
> Sorry but that concept of reliability is based on flawed logic. (By 
> the same logic, buying multiple Lotto tickets would greatly increase 
> my chances of hitting it rich)

I'm afraid your logic is flawed, Ralph. Of course buying multiple 
tickets increases your chances.

> For the RAID to fail, only one drive has to fail. So the MTBF for the 
> Array is the same as any single unit.

Wrong. It's easy to conceptualize with small numbers. Assume that one 
drive has a 10% chance of failing after 1 hour of use. That means that, 
if you run 10 drives for 1 hour, chances are 1 will fail. So what 
happens if a RAID-0 formed of 1 drive runs for 1 hour? Its chances of 
failing is the same as for 1 drive. But what if your RAID is made up of 
10 drives? Chances are that, after 1 hour, 1 drive will fail. But if 
your RAID is type 0, 1 failure means the failure of the entire array. 
So each time you add a drive to this kind of RAID, you increase the 
chances of failure.



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