DARC: design and evaluation of an I/O controller for data protection

Lately, with increasing disk capacities, there is increased concern about protection from data errors, beyond masking of device failures. In this paper, we present a prototype I/O stack for storage controllers that encompasses two data protection features: (a) persistent checksums to protect data at-rest from silent errors and (b) block-level versioning to allow protection from user errors. Although these techniques have been previously used either at the device level (checksums) or at the host (versioning), in this work we implement these features in the storage controller, which allows us to use any type of storage devices as well as any type of host I/O stack. The main challenge in our approach is to deal with persistent metadata in the controller I/O path. Our main contribution is to show the implications of introducing metadata at this level and to deal with the performance issues that arise. Overall, we find that data protection features can be incorporated in the I/O path with a performance penalty in the range of 12% to 25%, offering much stronger data protection guarantees than today's commodity storage servers.