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Chunkfs: Fast file system check and repair

Chunkfs is a file system designed to be incrementally checkable and
repairable. Disk capacity is increasing faster than the ability to
read the disk, to the point that in a few years, a normal laptop will
take several hours to check any existing file system. Chunkfs is the
first file system design that will allow the file system to be
incrementally checked *and* repaired, bringing average fsck time down
to minutes or seconds. According to our estimates, the same
average-size laptop file system in 2013 will take 80 minutes to check
and repair using ext3, but only 5 seconds to 3 minutes with chunkfs.
Chunkfs is not a reimplementation of any existing file system; it is an
original architecture first implemented in Linux.

Chunkfs divides disk space up into chunks (surprisingly enough), each
of which contains an independent client file system. The client file
systems are glued together with "continuation inodes" - a structure
with forward and back pointers between connected inodes - so that
files and directories can grow larger than an individual chunk, but
keep the metadata of each independent. The result is that when the
file system gets corrupted, in most cases only the corrupted chunk and
its continuation inodes need to be checked, and the data in the other
chunks is safe. Corruption will be detected by checksums, I/O error
return codes, and disk-level error reporting.

Chunkfs is currently in active development, sponsored by EMC
Corporation. The code base will be available for public development
in August 2007. Chunkfs will be usable as a root file system by LCA.

This presentation will be accessible to the average LCA attendee, but
include enough detail to satisfy the kernel hacker. Besides
big-picture explanations, there will be code walk-throughs and demos
of chunkfs file systems detecting and fixing corruption.

Project: chunkfs 


Valerie Henson

Valerie Henson has been writing Linux kernel code since 2000 and remembers fixing file system corruption on ext2. She was one of the architects and implementors of Sun's ZFS file system. She recently started VAH Consulting, LLC, a Linux kernel consulting company specializing in file systems. She writes the Kernel Hacker's Bookshelf series for Linux Weekly News because she cannot bring herself to write a blog. She maintains the TCP/IP Drinking Game.

Valerie Henson

Valerie Henson has been writing Linux kernel code since 2000 and remembers fixing file system corruption on ext2. She was one of the architects and implementors of Sun's ZFS file system. She recently started VAH Consulting, LLC, a Linux kernel consulting company specializing in file systems. She writes the Kernel Hacker's Bookshelf series for Linux Weekly News because she cannot bring herself to write a blog. She maintains the TCP/IP Drinking Game.

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