Why microSD Cards Get Slower Over Time — And What You Can Do About It
The performance drop most people blame on “bad cards” is usually normal behavior.
If you’ve ever had a microSD card that felt fast when it was new but frustratingly slow a year later, you’re not imagining things. This is a real, measurable behavior in flash storage, and it happens even with reputable brands. The important part is this: most of the time the card isn’t “broken.” It’s just working harder internally than it used to. In fact, real-world reporting shows reliability issues across removable flash are becoming more common, with USB flash key failures increasing by over 300% in recent years.
The slowdown usually comes from the way flash memory manages itself over time, not from sudden damage. And once you understand what’s happening inside the card, you start to see why some use cases age gracefully while others fall off a performance cliff.
A simple mental model helps.
Think of your microSD card as a warehouse
Picture your microSD card as a warehouse full of boxes. Each box represents a piece of data. The shelves are the flash memory. The warehouse manager is the controller inside the card. The manager has one annoying rule they must follow: once a box is placed on a shelf, it cannot be edited. If something changes, a new box must be placed somewhere else and the old box is marked as obsolete.
That rule isn’t a metaphor. That’s how NAND flash actually works. Flash cannot overwrite data in place. Every change becomes a new write somewhere else.
Early on, the warehouse is empty. There’s space everywhere. New boxes get placed quickly. The manager barely has to think. Performance feels fast and effortless.
Over time, more shelves fill up. Old boxes pile up. Some shelves contain a mix of useful boxes and obsolete ones. Now the manager has more work to do. They must constantly decide which shelves can be cleaned, which boxes must be moved, and where new boxes can go. That housekeeping work happens in the background, but it competes directly with your read and write requests. That’s where performance starts to slide.