how long should it take to write zeros to disk??

[blueleaf]

hello
i've got a little stuck with the whole 'using disk utility to erase the drive' thing...(i know its probably really simple so please forgive me if i'm being somewhat dense about this!) as its telling me its going to take 145 hours to write the zeros to disk and i kind of think thats not quite right...maybe?! (it was 75 hours but i decided to try to start over - ie. i selected the skip button and now its even worse...oh dear)
i have a new WD external hard drive connected by usb (400 gb) if thats of any help and it didn't have anything on it but was grayed out in the destination box....hence the erase bit.
any help much appreciated!

[dnanian]

It might be going slow because of USB, blueleaf: that's one reason we suggest FireWire drives.

[blueleaf]

It might be going slow because of USB, blueleaf: that's one reason we suggest FireWire drives.

i've only just seen this - so i'm sorry (i guess thats what happens when you post things twice....though i was asked to log in again just as i was posting it after which two posts appeared?! very strange.)
anyway i guess this partly answers my question though unfortunately i had already purchased the usb drive before finding out about and purchasing super duper today.
i still don't understand why its taking twice as long now and i feel concerned about leaving the computer running constantly while this process takes place - any thoughts?
thanks again for your help.