[RFC] Copy on First Read?

[Roger Larsson <roger.larsson@norran.net>]

I have been thinking about a file system that uses Copy On First Read.
My idea looks like this:

1. Split the disk in three parts (unused, write, used - could be growing from 
top and bottom like heap and stack)
2. Writes goes to one part - log structured, like a tape. Fragmentation of 
files are OK, but buffering is done to prevent the worst cases.

This to allow fast write of huge amounts of data.

Later when the file is first read
* the size is known.
* is probably read together with other files that in future will be used
   together.

So the allocation rule for the copy on first read can use these facts.
Only files that are actually used will be read and thus rewritten.

This will leave unused files in the write part. This old files can be 
compacted to and moved to the 'unused' part to give a continuous area to
use as write part. These files could even be moved to a slower media
(if available).

Log files will remain in 'write/unused' sections until searched.

Comments?

/RogerL