Laurie wrote:
> (spanning). I understand what RAID 1 (mirroring) is and how
> it works; but I really do not understand how RAID 0 works or
> what parallel operation of the two drives on the channel means
> and entails.
Striping simply means that data is interleaved on different disks. In a
simple two disk stripe set, you interleave between two drives. When the
file is read or written, you're using both drives, so (in an ideal world)
you get twice the speed of a single drive. In practice it's not quite double,
but it can be close.
>While it may be different for third party RAID controllers, the manual
for
>the RAID controller on the ABIT KG7-RAID motherboard says that you need
4
>drives to use RAID 0+1 and that the second pair duplicate the first pair.
In RAID 0/1 you have four drives - two sets of interleaved drives, with
the data mirrored between the pairs. So you get the speed increase of striping
plus the security of mirroring *but* you lose storage space by mirroring.
If you have two 20GB disks interleaved, you get 40GB of storage with almost
double the speed. Mirrored you have normal speed but greater security.
To get the combination you have the expense of four 20GB drives giving
you 40GB storage with security and speed.
A better system with multiple drives is RAID5 where you have "parity" -
it's a bit complicated to explain but in RAID5 any of the drives can go
down and you can rebuild the data from the other drives. This sort of thing
tends to be expensive to set up, just like 0/1!
IMO the higher RAID types are fine for servers, but not worth the hassle
for home use. I think for home/SOHO use with film scanning, go for striping
to get the speed and if you're worried about security, get a tape drive
for backup.
Rob
Rob Geraghty harper@wordweb.com
