Data degradation

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Data degradation is the slow loss of data quality on storage devices over time, even if you don’t use the data. It can happen on many kinds of media and is also known as data decay or bit rot.

How it happens by storage type

- RAM (DRAM): tiny errors can occur when a stored bit loses charge or is hit by particles. These “soft errors” can flip bits. ECC memory helps detect and fix most of these.

- Flash and SSDs: data are stored as electrical charges. Over years, charges can leak and the read thresholds can shift. Controllers test and rewrite data at different voltages to slow decay. Endurance is limited, but refreshing data helps keep it readable.

- Magnetic drives and tapes: magnetization can fade, especially at higher temperatures. Hard drives use error correction and can rewrite data to fix some errors. Tapes and older media are more fragile; frequent rewriting can help if the medium isn’t damaged.

- Optical discs (CD/DVD/Blu-ray): dye layers and backing can break down. Storing discs in a cool, dark, low-humidity place helps, and newer “archival” discs last longer, though nothing is truly permanent. Some tools can scan for decay before data becomes unreadable.

- Paper and printed media: paper degrades over time due to acids, heat, humidity, and pollutants.

- Other factors: data can be affected during streaming or transfer, and factors like software bugs, security incidents, improper handling, or aging hardware can cause problems.

What you can do to protect data

- Use error protection: hardware ECC, and file systems with integrity checks (for example, ZFS, Btrfs, ReFS).

- Create redundancy: keep backups, use RAID where appropriate, and store copies in multiple locations.

- Check and verify: regularly check data integrity with checksums or comparisons to other copies.

- Refresh data: rewrite data before it becomes unreadable, and follow recommended refresh cycles for the media you use.

- Choose durable options: for long-term storage, select media designed for longevity and monitor aging media for signs of failure.

There is no perfect solution, but combining redundancy, integrity checks, and periodic refreshing greatly reduces the risk of data loss from degradation.