This may have been mentioned before, but perhaps there could be a
"trickle-out" option along the lines of "if the hard drive is idle (and
optionally only if it's spun up), slowly write out the changes to the
disk structure." This could also be paired with keeping as much of the
data in memory as necessary to mantain the speed boost that r4 gets from
temporal locality of reference, possibly just giving it to the system
cache.
Hm actually, this looks a lot like read-ahead algorithms, but instead
it's "write-ahead" :
For instance :
- Sequential writes on large files should stream through the cache.
- Random writes or small file writes should be kept as long as possible
in dirty pages so they can be coalesced into larger writes with a better
disk layout on flush, or not written at all if it was temp files from a
make, for instance.
Do the file copying programs open their output files with O_SEQUENTIAL ?
If so, there is information to exploit...
