Improving Data Integrity In Linux Software Raid With Protection Information (T10-Pi)

The T10 DIF (Data Integrity Field) and DIX (Data Integrity Extension) specifications provide mechanisms to guarantee end-to-end data integrity and protection in the face of silent data corruption in modern storage systems. However, the Multiple Devices (MD) software RAID driver in Linux does not fully leverage these capabilities to provide such end-to-end guarantees with widely-used RAID modes such as 5 and 6, thereby causing an "integrity gap" in the Linux I/O stack. This paper describes the design and performance characteristics of a DIX-aware MD module that plugs this integrity gap with minimal overhead to client applications. A PI (Protection Information) operator is added in MD to handle the PI-related operations, and dedicated buffers for PI are allocated and managed in MD RAID-5/6 personality's stripe structures to generate, store, and verify the PI. This allows seamless exchange of PI information among end-applications running in user mode, file systems, the linux block layer, and PI-capable HBAs and drives. Our evaluations show that the DIX-aware MD module has the capability of detecting SDC with the tolerable performance penalty.