Posey's Tips & Tricks
Why Not Use SD Cards for Data Backups?
SD cards may be cheap and portable, but their limited write endurance, greater risk of corruption and physical loss, uneven long-term reliability, and poor cost-per-capacity make them a weak choice for dependable data backups.
I recently had someone tell me that they had started backing up their data to an SD card. On the surface, backing up your data to an SD card seems genius. After all, the cards are inexpensive, portable and they have a large capacity. Even so, using an SD card for data backups is probably a bad idea (although infinitely better than not having a backup at all). Let's talk about some reasons why SD cards probably aren't the best backup medium.
One of the biggest reasons why I would not recommend backing your data up to SD cards is that the cards have a limited lifespan. Several years ago, I was recording a lot of video using GoPro cameras. At first, I was reusing SD cards, simply blanking the cards prior to the start of the next project. Over time however, I began to notice that the cards were beginning to degrade and that frames were being dropped during the recording process. The reason for this is that like an SSD hard drive, an SD card can only endure a certain number of write cycles. Repeatedly backing up data to the same SD card will quickly wear out the card, eventually leading to data loss. Needless to say, I eventually stopped reusing SD cards and instead, use a brand new card any time that I am going to be recording something that matters.
Another reason why it might be a bad idea to back up data to an SSD card is because the cards are comparatively more likely to suffer data corruption than other types of backup media. This is not to suggest that SD cards are unreliable. It's just that things like sudden power loss, improperly ejecting a card, or even software glitches can easily result in data corruption. While the same can also be said for other types of removable media, my own experience has been that SD cards just seem to be a bit more fragile than tapes or external hard drives. Never mind the fact that modern backup systems use redundancy to protect against media failures. As an example, backup servers almost always use RAID arrays or erasure coding as a way of guarding against disk failure. Conversely, SD cards do not offer any such safety net.
And speaking of being fragile, some SD cards seem to be prone to long term bit rot, but the opposite can also be true. I have had SD cards fail relatively quickly, but I have also had SD cards with extreme longevity. I recently found an old digital camera in my closet and there was still a memory card in the camera. I inserted the memory card into my computer and found that it contained photos of my grandparents, way back in 2005! Clearly, that particular card had been able to preserve data for over 20 years. On the other hand, I have also seen the opposite happen. I once went on a scuba trip and the memory card from my underwater camera failed before I even made it back home. And that's the problem. SD card reliability is unpredictable. A card might preserve your data for 20+ years or the card might fail almost immediately. You can hedge your bets by avoiding cheap cards, but it's impossible to know for sure just how long a card is going to last.
the small physical size of an SD card makes it easy to accidentally lose a card or to accidentally damage or destroy the card. Water, heat, and static electricity can all potentially damage a card.
Finally, SD cards might not always align well with the data that needs to be backed up. This can be especially true if you are using cheap or low capacity cards. Some such cards use older file systems, that are incapable of storing files greater than 4 GB in size. Similarly, a lot of the less expensive cards tend to be slow, meaning that it might take a long time to back up your data.
Of course, there are high capacity / high performance cards available. The largest card that I have personally seen was 1.5 TB. Amazon offers one such card for just over $200. Even so, you can get a portable hard drive with double the capacity, for a fraction of the price.
My personal take is that using SD cards for data backups is a bad idea. However, I will concede the point that you could theoretically build an effective backup strategy around the use of SD cards if you take all of the proper precautions and rotate cards frequently.
About the Author
Brien Posey is a 22-time Microsoft MVP with decades of IT experience. As a freelance writer, Posey has written thousands of articles and contributed to several dozen books on a wide variety of IT topics. Prior to going freelance, Posey was a CIO for a national chain of hospitals and health care facilities. He has also served as a network administrator for some of the country's largest insurance companies and for the Department of Defense at Fort Knox. In addition to his continued work in IT, Posey has spent the last several years actively training as a commercial scientist-astronaut candidate in preparation to fly on a mission to study polar mesospheric clouds from space. You can follow his spaceflight training on his Web site.