> > >However, there is no redundancy in a RAID0 set, hence it's more
commonly
> > >referred to as striping. Actually, introducing RAID0 increases the
> > >probability of a disk crash (and hence data loss without propper
> > >backup) by the increase in disks.
> > >
> What a theory is this?!
> How can it increate a probility of a disk crash? Is it just because of
using
> two disks?
> Is so, it is a nonsense.
Why is it nonsense?
Suppose the probability of a disk crashing is
"Once in ten years"
If you do repeated testing using a bank of ten disks, you would expect (on
average) a disk to crash every year. OR, if you're really unlucky, nothing
happens for ten years and then they all explode at exactly the same time at
the end of the tenth year (OBVIOUSLY this is unlikely). But one of the two
must happen - EITHER the probability of "ANY" of the disks crashing is
multiplied by ten because you have ten disks
- i.e. IF you know the probability of a single disk crashing is "once
in x years" then the probability of any one of "n" disks crashing is "once
in (x/n) years"
, OR the amount of data you lose at the end of the ten years is multiplied
by ten
- i.e. IF you know the probability of a disk crashing is "once in x
years" then you expect to lose one disks' worth of data after x years -
therefore if you have "n" disks the amount of data you lose after "x" years
is "n" disks's worth
In the first scenario, the probability of a disk crash is OBVIOUSLY
increased if you have more disks
In the second scenario, if you amortise those "n" disks crashing over "x"
years you easily calculate that, in ONE year you will have effectively (n/x)
disks crashing - which is the same as saying you will have ONE of those "n"
disks crashing effectively every (x/n) years. You can see this is exactly
the same statement as before
So either way you look at it, the probability that any one of your disks
crashes is dependent upon the number of disks you have.
As a second example, consider this. What's the probability of rolling a "6"
on a single dice? It's 1/6 , right?
Now what's the probability of rolling a "6" if you throw two dice
simultaneously? Either of the dice can turn up "6" - hey, with two dice
that means you're twice as likely to get a "6"!
- What's the probability of rolling a "6" if you throw 36 dice
simultaneously? You actually have a 600% chance of throwing a "6"! What
that means is, on AVERAGE, you will expect to throw six "6"s every time you
toss all 36 dice.
It's not nonsense, just basic probability theory.
> > Yeah, thats true, but for my home system, i'm not too concened about
> > redundency, although this m/board can do raid0+1, but i backup a few
> > of the things i want to keep, erm... sometimes <g> its not worth the
> > cost of loosing the extra disks, most stuff i can re-install
> >
> What data loosing are you talking about? I think hard drive failure is not
a
> common problem
> (compared e.g. to strange problems of M$ Anything <enter any year here>)
> Or not?
hard drive failure is more common than maybe you think... hard drive
manufacturers five years ago were quoting mean time between failures (MTBF)
that meant that, if you ran their drives practically non-stop for
approximately three to five years, you would expect media errors, drive
mechanical errors and bus errors to occur at least once.
I know this because, among other things, our company supplies Audio-Visual
equipment to telephone operators to record calls and supply live audio
feeds, and the disks we started supplying three-to-five years ago and now
starting to fail with alarming regularity...!
And of course, if a drive starts to fail, it's only gonna get worse ...
reformatting can only help /so much/ ...
> btw. Is better 133MHz bus with ATA100 drive - or - 100MHz bus with ATA66
> drive?
Hmmm, let me see.
133MHz with ATA100 drive is better because
- The bus runs at 133MHz instead of 100MHz
and
- The drive controller uses an ATA100 spec instead of an ATA66 spec
:)
(What did you expect me to say? ;OD )
Dave
