> It *IS* more unsafe to use RAID0. And MTBF *IS* additive.
>
> No and no. I designed SCSI controllers and disk subsystems (for the
> storage
> division of one of the top computer manufacturers) for years, as well
> as
> tested disk subsystems. I know how MTBF is determined.
Seems like you have done everything and also know everything. I don't
know how your company (or you) determined MTBF of a RAID0 system but
most companies as Compaq, IBM, Sun, Adaptec, etc. say that MTBF will
decrease. Exactly because of the reduced MTBF of a system with multiple
HDs Berkeley has suggested the RAID system. The RAID system is supposed
to relax the impact of the reduced MTBF. That doesn't mean the MTBF
becomes higher when a RAID system is deployed but it just makes it more
likely that the failure can be repaired. That is not the case for
RAID-0 though which is why many people said that RAID0 does not really
belong to RAID which asks for redundant drives (which are obviously
non-existent in RAID0).
I see though where your (company's) calculation might come from. You
can determine MTBF for a certain device by testing for example 10000
drives for 1000 hours and then divide the total of 10000*1000 hours by
the number of failures. That way you don't have to test one drive for a
long time (it's lifetime and then replace it with a new one).
Nevertheless, this calculation doesn't apply to RAID as a RAID system
has to be considered as a single identity. So you cannot claim that
because you have 10 HDs your RAID system is working 10*1=10 hours in
each single hour. Your RAID system is ONE identity and therefore is
working only 1 hours each hour it is up. Therefore the MTBF decreases.
Nevertheless, the reliability of HDs are quite high these days and
therefore I wouldn't hesitate to have a RAID0 system with a couple of
HDs for my imaging purposes and adequate backup. As a matter of fact, I
am considering updating my computer system and in that case I am going
to setup a RAID0 system with two fast 80GB.
End of discussion on my side.
Robert
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