I have an idea that I could implement through Google's "Summer of Code"
project, but as I have little experience with stuff it involves (kernel
programming / disks / filesystem optimization), so I expect any answer
from "It won't work" or "It's useless" to "It can't be done". :)
The idea is this: to implement sort of GEOM-layer disk data journaling
system. I imagine it to be a GEOM class using two "lower-level" devices:
one for data and one for the "journal" (this way, the journal device can
be on a fast and small disk). Such journaled device could be used to
host any filesystem, probably mounted with synchronoues-access, and it
will result in faster write access by keeping the writes sequential in
the "journal" device. Journal information will be commited to the data
disk periodically by a separate log-writer thread, or when it gets full.
The "data disk" will be consistent so it can be used without it's
"journal" part (after a clean disconnect/rebuild) if needed. At the
worst case, I think this will help performance in cases when there's a
burst of write activity followed by a period of IO idleness.
I've made the above idea more-or-less from my head in one afternoon, so
it's perfectly possible that I'm missing some vital point or that it's
complete nonsense :)
Does it make sense to do it this way? Is it worth applying for the SoC?
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