If you actually care about the NSA or KGB doing a low-level magnetic scan to recover data from your disk drives, you need to be using an encrypted file system, period, no questions. There are occasional articles that pop up on the net talking about somebody's improved capability for data recovery.
If you're part of a US government agency with NSA or DoD rules, that isn't necessarily required, or approved as adequate, but that's strictly an issue of their flexibility. On the other hand, if your threat model includes the Mafia, you might want to get some steel kneecaps pre-installed. It's been a long time since I've read any official regulations on this topic, and at the time they were mostly for declassifying equipment that formerly held classified data: - either use physical destruction, or - use an officially NSA-approved Big Magnet, or - use software that's been approved by your security officer for your operating environment and remember that you need to wipe memory as well. My reaction to letting any NSA-approved Big Magnets near any of *my* computers was "absolutely no way - keep them outside our TEMPEST shield so they don't bother my working disk drives.":-) And I was never convinced we'd find officially-approved disk-wiping software that would actually run on Unix as opposed to VMS and wouldn't require immense reams of paperwork to get permission for. But our building had a machine shop in the basement, so when the sysadmin after me decommissioned the VAX, she got to help sandblast the disk drives. I don't know what they did about RAM, if anything. Most sysadmins in those days had wall decorations made from the disk drive platters with nice stripes on them left by the head crash. Hers was sandblasted smooth metal :-) Our standard on AT&T 3B2 computers was to wipe memory 3 times, and there was a special program that would wipe half the RAM, relocate itself into that half, and then wipe the other half, using first 0s, then 1s, then a (fixed? random?) bit pattern.
