VOSpace vs WebDAV

[Walter Landry]

Brian Major <majorb at nrc-cnrc.gc.ca> wrote:
> Hi everyone,
> 
> Here at the CADC we have had similar talks about VOSpace, but not
> necessarily about how it compares to WebDAV.  A question we are trying to
> answer is "What does VOSpace offer for astronomers?"  Indeed, there is very
> little in the specification that is specific to astronomy.  It is a
> well-designed, general-purpose virtual storage system specification.
>  However, there are some things to consider:
> 
> - There is real value in VOSpace Views.  This feature allows the CADC to
> deliver to the user only the bytes in which they are interested, not just
> whole files.

Thank you.  I had forgotten about this aspect of VOSpace.  I agree
that a sampling and conversion service is a useful thing to have.  In
fact, that is what the AccessData standard describes.  So I would
think it would be best to adopt AccessData for this kind of operation
separately from the data store.

> - The specification has been flexible enough to allow the CADC
> implementation to have customizations and optimizations in our supporting
> storage systems that may be running on heterogeneous infrastructures.  If a
> lower-level standard is adopted will there be such flexibility?

Just looking at WebDAV, it has even fewer requirements on the server
than VOSpace.  I do not think this is a problem.

> That said, I agree with Dave here--I think it's time to step back and look
> at the big picture and the role and look of VOSpace in the future.
> 
> Here are some technologies/articles you may find interesting that pertain
> to this discussion:
> 
> - A federated storage system build on WebDAV: Dynamic Federations  (
> http://www.dynamicfederation.org/DynFed/Welcome.html)
> - An similar article on that here: https://indico.cern.ch/event/218328/  I
> think you can substitute "HEP" with "Astronomy".

For those who have not looked at these HEP slides, they have
implemented a service with WebDAV plus "extras, WAN transfers, 3rd
party copy...".  So I looked at the way they support 3rd party copies

  https://svnweb.cern.ch/trac/lcgdm/wiki/Dpm/WebDAV/Extensions

I do not see support for asynchronous transfers.  Bummer.  My guess is
that they decided it was too much work to do it properly.

Cheers,
Walter Landry