I’m in the middle of a process to prepare our venerable SAN disk subsystem for retirement. It served us well for the last six years. Due to confidentiality of data once stored on this system I opted to erase data by first formatting all logical volumes at OS level, followed by erasing data with specialized tool that writes random data with the choice of several runs and finally formatting all volumes low-level with SAN management tool. Step two and three are time consuming parts of the process, that will take approx. 3 full days. And I’m wiping out a mere 1.6TB system!
If you’re looking for specialized tool for destroying data I suggest that you start here. Depending of the platform choose the most appropriate tool. I tried Eraser for Windows and it performed well. I think this is another tool to add to my list of the free open source software that I use.