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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 MADext2. Backup MAD enhances dependability of file system by protecting disk pointers on behalf of file system.

Keywords: file system, reliability, disk pointer corruption, disk pointer types, disk pointer snapshot, in-partition restoration, out-of-partition restoration, OS-aware recovery, ordered recovery

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Received August 26, 2010; revised November 20, 2010; accepted January 12, 2011.
Communicated by Tei-Wei Kuo.
^* This research was supported by the MKE (The Ministry of Knowledge Economy), Korea, under the ITRC (Information Technology Research Center) support program supervised by the NIPA (National IT Industry Promotion Agency) (NIPA-2010-(C1090-1011-0004)). The preliminary version of this paper has been partly presented at the 9th USENIX Symposium on Operating Systems Design and Implementation (OSDI¡¦10) Poster session, Vancouver, BC dated on Oct/04/2010 with poster title ¡§Backup Metadata As Data: DPCTolerance to Commodity File Systems.¡¨
⁺ Corresponding author.