Re: [RFC] Copy on First Read?

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

On Monday 10 July 2006 10:27, Andreas Dilger wrote:
> On Jul 10, 2006  09:04 +0200, Roger Larsson wrote:
> > I have been thinking about a file system that uses Copy On First Read.
> > - - -

> It doesn't sound significantly different than a regular log-structured
> filesystem.  You still need a cleaner thread to move files around and
> keep the free space contiguous.

It is needed but shouldn't have that much to do. Unless most files are
never read...

> Since this is (in essence) data journaling 
> all writes, you need to have double the disk bandwidth in order to rewrite
> all of the files that are read.

Not double since it is only the first read after a write that needs to be 
rewritten. My assumption is that most files are written fewer times than
they are read. And the read for the copy is free since that was what
triggered it.

Config files - few changes, many reads.
Media files - one write, (probably) many reads.
Office files - more reads than writes.
Log files - many writes, few reads.
. . .

/RogerL