[MINC-development] Welcome

[Steve ROBBINS]

On Tue, Nov 19, 2002 at 09:32:13AM -0500, John G. Sled wrote:
 
 
> On Tue, Nov 19, 2002 at 01:19:55AM -0500, Steve ROBBINS wrote:
 
> > > 6. Given #3, block-structuring MINC data will improve file access speed.
> > 
> > ... for some access patterns.  It may degrade other access patterns,
> > e.g. traditional voxel_loop processing.
> 
> I don't think that voxel_loop would be affected by this since the loop
> could proceed through the voxels in their natural (i.e. file) order for
> most cases.

I probably should not have mentioned voxel_loop.  What I actually had in
mind was something like a convolution operation: you need to drag a
5x5x5 window across the volume, for example.  

I'm not an expert in these matters, but the naive approach of scanning
through the volume with a five-slice cache would be better served with
the current disk layout.  Is that not the case?

Even if that is the case, a different layout may indeed be so much faster
in some situations that it is an improvement overall.  I don't know.
I would be surprised if it is a win in _every_ case, and it would be
nice to know a bit about what the tradeoff is.


By the by, it turns out that HDF5 implements "chunked" storage and
sparse storage already.  And they have some kind of caching mechanism
in the library.  There is a small study on how the cache parameters
affect the read and write efficiency: 

  http://hdf.ncsa.uiuc.edu/HDF5/doc/Chunking.html


-S