Re: What is the point of RAID?
On Wed, Nov 12, 2008 at 3:44 AM, lee <lee@yun.yagibdah.de> wrote:
> Do you mean it is more likely that any one drive in the array fails when
> you have more drives, or do you mean that it is more likely for a drive
> in the array to fail when you have more drives? If drives fail more
> often when being used in an array with more drives, what makes them
> fail more often under those conditions?
It's purely a statistical property, not related to being in a RAID
array. But if there's (say) a 5% chance for a given drive to fail on
a given day, there's a 95% chance it won't fail.
If you have two drives, the chance *both* won't fail is the chance of
one not failing, times the chance of the other not failing -- 95%
times 95%, or 90.25%.
With 24, the chance of all the drives not failing is .95^24 or 29.2%.
Of course I just made the rates up, the survival chances of individual
drives are higher. But logic holds; the more drives you're watching,
the more lucky you'd have to be for none of them to be a dud.
-jeff
Reply to: