# Persistent Storage management

> RAM-only databases offer highly predictable response times, but real-time systems often require persistent storage as well. That’s where Flash Memory devices come in—they provide high-density, non-volatile storage at a lower cost than other persistent storage options. However, while flash is an attractive solution, its architecture introduces unique challenges for managing transaction deadlines. Processes like wear leveling, garbage collection, and bad block management (BBM) and error correction codes (ECC) can cause unpredictable delays, making it difficult to guarantee strict timing requirements for transactions. While flash memory hardware itself offers stable and predictable access latency maintaining logical data integrity requires a layered approach. Flash devices’ low-level drivers typically handle BBM, ECC, and CRC, while higher-level address translation and consistency management are handled by Flash Translation Layers — FTLs. This layered architecture—often referred to as the persistent storage stack—abstracts the physical characteristics of flash and presents a consistent, block-level interface to higher software layers such as embedded database systems. This enables reliable and time-bounded access to data in real-time environments. To understand flash’s role in real-time database performance and eXtremeDB/rt transaction predictability, it helps to take a closer look at Flash internal structure, and operational behavior, and the different types of flash memory and its connectivity options.

> - How Flash Memory affects predictability
> - Managed vs. Unmanaged NAND: Choosing the Right Approach
> - Storage Stack Options