ACM Transactions on Storage (TOS), Volume 11 Issue 1, February 2015, Article No. 4
Abstract:
Existing space management schemes for flash-based Solid State Drive (SSD) operate either at page or block granularity, with inevitable limitations in terms of memory requirement, performance, garbage collection, and scalability. To overcome these limitations, we proposed a novel space management and address mapping scheme for flash referred to as Z-MAP, which manages flash space at granularity of Zone. Each Zone consists of multiple numbers of flash blocks. Leveraging workload classification, Z-MAP explores Page-mapping Zone (Page Zone) to store random data and handle large number of partial updates, and Block-mapping Zone (Block Zone) to store sequential data and lower overall mapping table. Zones are dynamically allocated and mapping scheme for a Zone is determined only when it is allocated. Z-MAP uses a small
part of non-volatile memory (Flash or Phase Change Memory) as streaming Buffer Zone to log data sequentially and migrate data into Page Zone or Block Zone based on workload classification. A two-level address mapping is designed to reduce overall mapping table and address translation latency. Z-MAP classifies data before it is permanently stored into flash memory so that different workloads can be isolated and garbage collection overhead can be minimized. Z-MAP has been extensively evaluated under various I/O intensive workloads. Our benchmark results conclusively demonstrate that Z-MAP can achieve up to 76% performance improvement, 81% mapping table reduction, and 88% garbage collection overhead reduction compared to existing FTL schemes.