According to Apple’s support document, if you own a previous-generation MacBook Air (sold from June 2012 through June 2013) with a 64GB or 128GB solid-state drive, you may have received a faulty storage unit. Thankfully, you don’t have to trek down to an Apple Store to have your drive tested – you can do it right from your computer.
If you have a potentially-affected device, visit the Mac App Store’s Updates pane and download MacBook Air Flash Storage Firmware Update 1.1. That will run a test of your drive; if it comes up faulty, then it’s time to make an appointment with your resident Apple Store or Authorised Service Provider, or call Technical Support.
If you don’t have time to do this right away, don’t panic: The program currently covers faulty MacBook Air drives for up to three years after date of purchase. But given that your Mac may potentially have problems with its drive – where you likely store most of your important information – you may want to check sooner rather than later. If your drive is affected, but you can’t have it fixed immediately, Apple recommends holding off on installing any software updates and making sure that your backups are up-to-date.