is cache-only-prefixes an nnpfs limitation?

[Pavel Cahyna]

Hello,

sorry for replying to this old thread...

On Sun, Apr 09, 2006 at 10:00:09PM +0200, Tomas Olsson wrote:
> Adam Megacz <megacz at cs.berkeley.edu> writes:
> >   - Do remote-filesystem file have to map 1:1 exactly to local files?
> >     Or do remote blocks map to local files?  Or do remote blocks map
> >     to local blocks?
> >
> Traditionally it's 1:1 for data, plus possibly some lookup sugar. nnpfs
> just has one "cache file" handle per fid.
> 
> For the current block prototype we use the same idea, but just split data
> in fixed size chunks in the simplest possible way and use those cache files
> as we use the single file today.  The chunk size is configurable but
> assumed to be a power of 2.  For some reason I'm also assuming a 1:1
> mapping between (fid, offset) and cache "block" file.

I have an idea, could the 1:1 mapping stay, with the cache file becoming a
"sparse file"?  The "holes" would fill the part of the cache file that
does not contain valid data.

Pavel Cahyna