wiping disks

I have an alphaserver 4100 with a rack of attached disks,
which our site regulations dictate I must clean the disks of before
I turn over to excess.

I am booted under single user mode at the moment, using

dd if=/dev/zero of=/dev/rzxxc bs=512 seek=1

Have done two of six of these disks so far, but it is taking >12 hours 
for something that's only an 18Gb disk.

Any way to do it faster?
Also, once I get all the scratch disks wiped, what's the easiest way to
wipe / and /usr?  boot off CD? Or can I use the existing OS install
to wipe the disk from under me, dying in a glorious panic when the dd
command returns?

Steve



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Steven C. Timm, Ph.D  (630) 840-8525  [email protected]  http://home.fnal.gov/~timm/
Fermilab Computing Div/Core Support Services Dept./Scientific Computing Section
Assistant Group Leader, Farms and Clustered Systems Group
Lead of Computing Farms Team