is cache-only-prefixes an nnpfs limitation?

[Harald Barth]

>   "There is just one reson that one should have blockcache.  You want
>    to edit filer larger then you blockcache"
> 
> Actually, I'm most interested in block caching for a different reason
> -- I often store large media files in AFS and seek around in them (ie
> access starting at random locations in the file).  Many of these files
> would fit in my disk cache, but moving the entire file over the
> network or crowding (almost) everything else out of my local cache
> would be bad.

Correct, users sometimes want to do other operations than to start
reading from the beginning, but a block cache is not needed just for
the feature "random read". For example there could be a file with
holes which would be filled when needed. Files bigger than the cache
happen sometimes (not often though), but for these rare cases block
caching is needed.

I think Tomas answered all the other questions.

Harald.