Article 5 - Wear Levelling

The moment you first use a flash drive it will have a limited number of times that data can be written to it. Typically this finite number of read cycles will be a lot (up to perhaps 100,000) however it does mean that, despite what many people think, a solid state device is not going to last forever.

With this in mind you are well advised to NOT rely on a single flash drive as a sole storage for critical data. The policy should always be to keep multiple backups for data that is irreplaceable.

One method of prolonging the lives of these devices is a process called wear levelling where the device will allocate the data chunks evenly over the entire device. This ensures that one particular zone of the Flash NAND chip doesn't get ordinarily worn by having data continuously written to it. If a device only has a few files on it and these were consistently written to the same zone then the chances of likely failure is increased.

As a process Wear Levelling works by the "controller chip" allocating the data to the Flash NAND chip either statically or dynamically.

The purpose of this article isn't to go into too much detail about wear levelling, more to warn users of these extremely handy devices not to rely on them  as unlikely to fail. Like any manufactured device, despite any inbuilt systems to negate failure, they can and will fail at some point in the future. The secret is for you to have decommissioned the device before it fails on you causing stress and data loss. 

If the device does fail then the chances of a successful recovery are extremely good, but as they say prevention is better than cure. 

posted 08/03/09