RAID 5 Equation

[Bill Clark]

RAID 5 parity is not on anyone particular disk.  That would be RAID 3 that
Mick is describing.  In RAID 5 the parity is spread out and shared across
all disks.  That is why RAID is so popular.  The odds are you won't loose
more than one disk at a time.  In most hardware RAID implementations if a
disks dies.  Then yanking the disk and replacing the disk will start the
rebuild of the parity redundancy and within minutes you can be fully
resillilent again.  Or if you have a designated hot spare it can
automatically take the place of a bad disk.

If you have 3 disks and they are all 9GB disks then your effective capacity
for that set is 18 GB.  Three disks is the minimum number of disks allowed
in RAID 5.

Bill
----- Original Message -----
From: Hanasaki JiJi <hanasaki at hanaden.com>
Cc: Kclug at Kclug. Org <kclug at kclug.org>
Sent: Tuesday, October 01, 2002 7:50 PM
Subject: Re: RAID 5 Equation

> So in Raid 5 the parity recovers data as well as identifying if data has
> been corrupted?  There was some equation, years ago that started:
> - 1 bit parity identifies an odd number of bit errors
> - 1 bit parity misses an even number of bit errors
> - 2 bits parity ....  BUT ITS NOT LINEAR, ITS EXP
>
> So what if the partity disk bites it?
>
> Mick Ohrberg wrote:
> > Theoretically, providing all the disks are the same size, it's the total
sum
> > of all disks, minus one disk (the parity disk).
> >
> > /Mick
> >
> > | -----Original Message-----
> > | From: owner-kclug at marauder.illiana.net
> > | [mailto:owner-kclug at marauder.illiana.net]On Behalf Of Jeremy Fowler
> > | Sent: Sunday, September 01, 2002 4:27 PM
> > | To: Kclug at Kclug. Org
> > | Subject: RAID 5 Equation
> > |
> > |
> > | Anyone know off hand the equation used to find the usable storage
space
> > | available with RAID 5?
> > |
> > |
>
>
>
>