I will be presenting a paper at the upcoming USENIX FAST conference
about using the ext3 file system journal to guide the software RAID
resynchronization process. I was wondering if you had any opinions
as to the viability of this approach in Linux.
Here is a link to the paper:
http://www.cs.wisc.edu/adsl/Publications/fast05-journal-guided.pdf
and the abstract:
We investigate the problem of slow, scan-based, software RAID
resynchronization that restores consistency after a system crash.
Instead of augmenting the RAID layer to quicken the process, we
leverage the functionality present in a journaling file system. We
analyze Linux ext3 and introduce a new mode of operation, declared
mode, that guarantees to provide a record of all outstanding writes
in case of a crash. To utilize this information, we augment the
software RAID interface with a verify read request, which repairs
the redundant information for a block. The combination of these
features allows us to provide fast, journal-guided resynchronization.
We evaluate the effect of journal-guided resynchronization and find
that it provides improved software RAID reliability and availability
after a crash, while suffering little performance loss during normal
operation.
Thanks,
Tim Denehy
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