SSD wear leveling algorithms ensure that the entire disk is used evenly. Any block on the drive can be literally anywhere in the storage medium, even more so than with hard drives. Some SSDs have significantly more storage media than they report (over-provisioning), again for wear leveling.

In theory, SSD erasing is solved by TCG OPAL functionality. All data written to the disk medium is encrypted, whether or not it is taken advantage of by the user. The key it uses cannot be retrieved or set by the user. Tell the disk to change the key it uses and the entire device is unintelligible noise.

Some articles: http://www.techrepublic.com/article/erasing-ssds-security-is...

http://arstechnica.com/security/2011/03/ask-ars-how-can-i-sa...

Shouldn't the ATA Secure Erase command take care of properly blanking an SSD? (Assuming that its firmware can be trusted, of course.)

In practice, it's a bit more complicated, though - typically the BIOS (or is the operating system?) locks out Secure Erase and you have to hot-remove the drive and reconnect it before the drive will accept it.

> Shouldn't the ATA Secure Erase command take care of properly blanking an SSD? (Assuming that its firmware can be trusted, of course.)

It does that -- by clobbering the hw encryption key.