 While the price of SSDs has continued to decline over time, SSDs are () still more expensive per unit of storage than HDDs and are expected to remain so into the next decade.SSDs based on NAND Flash will slowly leak charge over time if left for long periods without power.This causes worn-out drives (that have exceeded their endurance rating) to start losing data typically after one year (if stored at 30 °C) to two years (at 25 °C) in storage; for new drives it takes longer.