I have a large number of HDDs which I have the intention to sell. So I need to erase them.
I was thinking to buy tool from Blancco or White Canyon. Which tool you advise me to buy? Maybe some other tool?
anyway... in general i would advise to use DBAN (or it's unofficial fork dban) to wipe complete disks:
it would be the universal method because it works from it's own bootable iso, is therefor platform independent, also free (as in speech and beer),... you only need to create a bootable media (CD, DVD, USB, etc.) and start from it.
an interesting option would be Ultimate Boot CD: it offers DBAN and a bunch of other interesting tools on one bootable CD.
BUT to make it clear, on SSDs (or other flash based media) every kind of "secure deleting" may be useless!
the worst case would be: you are erasing nearly nothing and just killing your device much quicker than necessary! ...this depends on the hardware (controller) of the device! - in this case your best chance would be a "built in firmware" or special software from the manufacturer.