Bit Rot
While researching my last post, I came across some rather startling information with regards to the reliability of SSDs for long-term cold storage from Jonathan Kehayias at SQL Skills:
Of the four SSD’s I had stored data on, 100% of them had data loss due to a phenomenon known as bit rot.
And…
You can’t write data to an SSD, disconnect it, store it in a “safe” location for years on end and expect the data to remain accessible. SSD’s require power and routine usage to allow the onboard controller to check cells and perform reprogramming to reduce the likelihood of bit rot.
And…
For solid state media, the NAND cells store data using electrical charges that can slowly leak electrons away over time.
But how long can an SSD be safely disconnected from power and still hold its data reliably? As I scoured the Internet looking for this answer, the information I found was all over the place. Anywhere from days to months to years. (Which in my mind is the same as saying, “Who knows?”)
Anandtech has a write-up on data retention that refers to a JEDEC slide deck with the following requirement standards for SSDs:
(Image from here)
You’ll notice that enterprise-class drives need to be connected to power more frequently than client-class drives. You’ll also notice that temperature is a factor, with higher temperatures leading to lower retention periods. Keep in mind that this is the standard; actual drives could exceed these specs.
Perhaps the old mechanical HDDs aren’t completely without use. I like what this poster had to say on the subject over on superuser.com:
For real long-term storage, you need to make frequent copies. A librarian once told me that archiving is copying.
(Image from here)
For more information on bit rot and prevention, check here and here.