[NTLUG:Discuss] Which filesystem & partitioning for a 9Terabyte volume?

[Neil Aggarwal]

Ralph:

One thing has never made sense to me.

The storage capacity of RAID 5 is stated as
N-1 where you have N drives.  That means
the redundancy information is stored in the equivalent
of one drive's worth of space.

How can that scale to a large number of drives?

Let me state it this way:  The size of the
redundancy data expressed as a percentage
of the data storage is 1/(N-1).

For 3 drives, the redundancy is 50% as
large as the data.

For 4 drives, it is 33%

For 11 drives, it is 10%

For 101 drives, it is 1%

As the number of drives goes up, the amount of
redundancy data goes down as a percentage of the
data storage.

In the case with 101 drives, how can one bit of
redundancy recover 100 bits worth of lost data?

Does the redundancy algorithm get better as the
number of drives go up?

Thanks,
	Neil

--
Neil Aggarwal, (832)245-7314, www.JAMMConsulting.com
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> > My understanding is that given N drives (where N must be at 
> least 3) you 
> >   "consume" the equivalent of one drive spreading the 
> redundancy data 
> > across all drives.  Assuming all drives are equal size, how 
> is losing a 
> > small drive recoverable but losing a big drive not?