SSDs prove difficult to securely erase

Creative Commons photo courtesy of PiAir's Flickr photostream

At this week’s Usenix FAST 11 conference on File and Storage Technologies in San Jose, California researchers published a paper examining the effectiveness of different secure erasure methodologies on Solid State Disks (SSDs).

SSD kit

The researchers, Michael Wei, Laura M. Grupp, Frederick E. Spada and Steven Swanson of the University of California at San Diego, came to several interesting conclusions:

  • ATA and SCSI command set features for securely destroying data on SSDs (“ERASE UNIT”) were available on only 8 of the 12 drives tested and were only successful on 4 of the drives.
  • Repeatedly overwriting the entire disk with multiple repetitions can successfully destroy data, but because of the Firmware Translation Layer (FTL), this is considerably more complicated and time-consuming than on traditional hard disk drives. Based on their results, it is an unattractive option for most organizations.
  • Degaussing SSDs does not erase any of the data stored on them. While SSDs do not use magnetic storage, there was some hope that the electromagnetism might destroy the electronics in the flash chips.
  • Single file sanitization, the ability to securely destroy one file on an unencrypted disk, is nearly impossible on SSDs. The paper claims that even the most effective file destruction methods may leave behind more than 4 percent of the original data.
  • Drives that are encrypted provide the most practical form of protection. Disks can be safely decommissioned by deleting the encryption keys from the Key Storage Area (KSA) and then running a full DoD compliant erasure to ensure the keys are non-recoverable.

Single file sanitization results from UCSD paper
I recommend reading the full paper if you are interested in the challenges related to safeguarding data on SSDs.

To properly secure data and take advantage of the performance benefits that SSDs offer, you should always encrypt the entire disk and do so as soon as the operating system is installed.

Securely erasing SSDs after they have been used unencrypted is very difficult, and may be impossible in some cases.

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Creative Commons image of SSD kit courtesy of PiAir’s Flickr photostream.