Wiping, degaussing and shredding all get rid of data, but they don’t work equally well on every device. Choosing the wrong method can leave data recoverable, or destroy equipment that could have been reused. Here is how to match the method to the device and to how sensitive the data is.
Three levels of data destruction
A widely used way to think about this comes from the US standard NIST SP 800-88, Guidelines for Media Sanitization, which many UK organisations also refer to. It describes three levels:
- Clear: overwriting the data so it can’t be read back with normal tools or recovery software. The device can be reused.
- Purge: using methods that defeat even laboratory recovery techniques, such as a drive’s built-in secure erase command, cryptographic erase or degaussing.
- Destroy: physically destroying the device, by shredding, crushing or disintegrating it, so it can’t be used again and the data can’t be recovered.
The more sensitive the data and the less control you have over where the device goes next, the further down that list you should go.
Traditional hard drives (HDDs)
Hard drives store data magnetically on spinning platters, so all three methods work on them:
- Overwriting every sector is effective on a healthy drive and lets the drive be resold or reused. It is less reliable on a failing drive, because damaged sectors the drive has stopped using can still hold old data.
- Degaussing exposes the drive to a strong magnetic field that scrambles the data. It also wipes the factory information the drive needs to work, so a degaussed hard drive is finished: it can’t be reused.
- Shredding destroys the platters themselves and gives you something you can see with your own eyes. It is the usual choice for drives that held highly confidential data, or for faulty drives that can’t be overwritten.
SSDs, USB sticks and memory cards
Flash storage works differently, and that changes the rules:
- Degaussing does not work. SSDs and flash memory don’t store data magnetically, so a degausser won’t erase them.
- Simple overwriting is unreliable. SSDs spread writes across spare memory the computer can’t see, so overwriting the visible capacity can leave copies of old data behind.
- Secure erase or cryptographic erase, run through the drive’s own firmware, is the right way to purge an SSD you want to reuse, provided it is done with the correct tools and verified.
- Shredding to a small particle size is the safe option for physical destruction. The memory chips on an SSD are small, so a shredder designed only for hard drives can leave chips intact.
Phones, tablets and laptops
Modern phones and tablets encrypt their storage by default. A full factory reset destroys the encryption key, which makes the old data practically unreadable, so a properly reset phone can often be reused or resold. Make sure the device is signed out of its account (Apple ID or Google account) first, otherwise it can stay locked to you.
Laptops vary. Many newer ones have encrypted SSDs, which makes cryptographic erase a good option, but older models and desktops often have unencrypted drives. If you are not sure, or the data is sensitive, remove the drive and have it destroyed.
Servers, RAID arrays and backup tapes
Servers usually contain several drives, and data from a RAID array is spread across all of them, so every drive needs to be accounted for, including spares and drives that were swapped out years ago and left in a drawer. Magnetic backup tapes can be degaussed or shredded.
What to ask for as a business
- A record of every device by serial number, so you can show which drives were destroyed and when.
- A certificate of destruction for your records. Under UK GDPR you need to be able to show that personal data was disposed of securely.
- A clear chain of custody if drives leave your premises, or on-site destruction if they must not leave the building at all.
- The right method for each device type, rather than one method applied to everything.
Which method should you choose?
As a rule of thumb: if the equipment is going to be reused inside your organisation and the data is low-risk, a verified wipe is usually enough. If the equipment is leaving your control, or the data is confidential, financial or personal, physical destruction with a certificate is the safer choice, and for SSDs it should be destruction to a small particle size.
See our data destruction and hard drive disposal and recycling services, or book a collection. You can also call us on 020 7064 4996 to talk through what you need destroyed.