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NetBSD-SoC: Improving RAIDframe parity handling

What is it?

The problem: when a NetBSD system using software RAID for protection against disk failures is shut down uncleanly (e.g., in case of a power failure or crash), then when it reboots it must rewrite all of the redundancy information on the disks — a process that can take many hours and impose a substantial I/O load on the system — even though only a very small portion of the data (or perhaps none at all) actually needs it. The project, then, is to modify the RAID driver (raid(4), an adaptation of the RAIDframe project undertaken at CMU in the mid-1990s) to keep better track of which parts of the disks are currently being written to, and thus may need to be cleaned up in case of a crash. However, if the bookkeeping information needed to achieve that goal is written to the disks too frequently, it will interfere with the writing and reading of the actual data and reduce performance all of the time, not just after a crash.

Status

2009-06-16: It's alive! And the most blatant bugs are gone, but chances are it's still doing something wrong. More testing is needed.

GSoC Timeline

Deliverables

Mandatory (must-have) components:

Optional (would-be-nice) components:

Documentation

(This section will be populated at a later stage in the project.)

Technical Details

(Coming soon.)


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Jed Davis <jld@NetBSD.org>
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