Customers should feel comfortable that their data is stored safely. Here is some documentation on FlashBlade Security.
All blades that are returned to Pure undergo a stress test which erases and overwrites the data in every block within the NAND. Any blade that does not pass the stress test (broken, too worn, etc) is destroyed. We also offer a non-return option. This is more expensive to the customer as Pure does not get the blade returned. The support process for determining broken parts is the same except the customer would be responsible for the destruction of the non-returned part.
Additional Reference: