[Nexus] Release of Version 2.0.0 (including HDF5 support)

[Mark Koennecke]

Brian,

On Mon, 16 Sep 2002, Ray Osborn wrote:

> On 9/16/02 12:33 PM, "Brian Tieman" <tieman at aps.anl.gov> wrote:
> 
> > Are there any driving reasons to use HDF5 over HDF4?  Does it provide better
> > performance?  Better compression?  Easier to handle files?  Increased
> > compatability? Etc...
> > 
  
   In addition to what Ray already mentioned: I have been forced to use 
   HDF-5 at two of our SINQ instruments because I hit HDF-4 limititations.
   The first is a four circle diffractometer with PSD, operated like a 
   protein crystallography rotation instrument. With this HDF-4 permitted
   me to store only 49 frames in one file because HDF-4's limit of 64000
   objects. I did not have that many datasets but apparently almost
   everything consists of many objects in HDF-4. HDF-5 solved this 
   limitation. 

   The second case is a reflectometer with a PSD operated in TOF mode. I
   get datasets of up to ~200MB here. In order to keep memory 
   requirements low and keep some kind of reponsiveness of my instrument
   control program I read this in chunks of 16MB from the histogram 
   memory and write it to file. HDF-5 now allows to use
   chunked datasets (or dataset slabs) together with compression which I
   obviously want on those datasets. HDF-4 only supports compression on 
   datasets which are written in one go. This is not working yet because
   of a bug in HDF-5 but the NCSA people promised to provide a fixed
   version in autumn. 
   
   This also means that HDF-5 and the new NeXus-API is stable enough to
   use it in a production environment.

			Regards,

				Mark Koennecke