Backup Metadata As Data: DPC-tolerance to Commodity File System
YOUNG JIN YU, DONG IN SHIN, HYEONG SEOG KIM, HYEONSANG EOM AND HEON YOUNG YEOM
School of Computer Science and Engineering Seoul National University 599 Gwanak-ro, Gwanak-gu, Seoul, Republic of Korea
Backup Metadata As Data (MAD) is a user-level solution that enables commodity file systems to replicate their critical metadata and to recover from disk pointer corruptions. More specifically, it extracts disk pointers from file system and saves them as user data. When some data blocks become inaccessible due to pointer corruptions, Backup MAD restores access paths to them either by copying the blocks to another file system or by directly updating on-disk structures of file system. The latter technique helps Backup MAD restore lost files faster than any other recovery solution because data blocks are not moved during restoration. Also, as the technique relies on disk pointers extracted from a consistent file system state, it can rescue up to 50% more files than a scan-based recovery tool that infers block dependencies from a corrupted partition. We demonstrate the effectiveness of our technique by two real implementations, MAD-NTFS and MAD-ext2. Backup MAD enhances dependability of file system by protecting disk pointers on behalf of file system.