[RFC 004] Operation Review Comment 5

Review of DAP2 operational experience:

NASA's Earth Science Data Systems Standards Process Group (SPG) is considering the Data Access Protocol, Version 2, (DAP2) for adoption as a community standard.  This is the second review of DAP2, this one focusing on its operation experience.� The questions below are provided to guide your feedback. You only need to answer questions applicable to you.  Please send comments to ese�rfc�004@spg.gsfc.nasa.gov.�

OVERALL COMMENT:� The statistics below refer only to one dataset we serve using OPeNDAP (AVHRR Pathfinder SSTs). We serve other datasets on OPeNDAP but not separately track their OPeNDAP actitvity for them.

1. Describe in a sentence or two your overall operational experience related to DAP2 (e.g., scientific analysis; science users, server operation; database management; or data translation, etc).� What kinds of DAP2 systems do you have experience with?� (e.g., OPeNDAP netCDF server, OPeNDAP HDF server, OPeNDAP Matlab Toolkit, Ferret, GrADS, and etc).
1. How long have you been using DAP2 operationally?

For two years.� We have been running and actiively using the netCDF and HDF servers with no problems.� �

2. What types of applications do you use DAP2 systems for?� Are the DAP2 systems applicable to your applications? (e.g., Do they work well with the data types and data manipulations in your application?)��
1. How many of your applications use DAP2?

                                                               i.      Total number of applications

                                                             ii.      Percentage of applications

We use the OPeNDAP server primarily as a way of serving data to more users.� We do not tend to use it in any internal applications NODC-wide. However, individuals here do use it occasionally with Matlab and fortran code.

3. Why do you choose to use DAP2 systems over other systems for your applications?
1. What alternative technologies did you consider?

We use it because it is well supported by the community, has lots of applications that work with it, and it is one of the technology standards for IOOS.� We are also considering Web Coverage/Map Services and will likely implement them someday as well, in an effort to serve more users.

4. Are the DAP2 systems easy to use?� (e.g., Is it hard to learn how to use DAP2 systems?)
1. How has the use of DAP2 affected your user support workload?

It is unclear.� There are relatively few requests from users on how to use the OPeNDAP server.� People either seem to know how to use it or not, though I recently spent some time with a user developing fortran code to access our data on the server.

5. Does the performance of the DAP2 systems you have experienced meet your requirements?� (e.g., Does it take a long time to access data in DAP2 systems?)
1. Have your bandwidth issues changed since you have been using DAP2 systems? (e.g., Have you seen increased bandwidth requirements because of increased data access or DAP2 overhead, decreased bandwidth requirements because of reduced data volume from subsetting, no impact on bandwidth because of low usage?)

Unknown, but I think our overall requirements have not changed much.� We are perhaps getting more data accesses, but the volumes being distributed via OPeNDAP are not known to us.

6. What operational challenges do the DAP2 systems present? (e.g., Does it require advanced processing power, large amounts of memory, complex configuration, etc.? Are the systems easy to deploy and maintain?)
1. How has the use of DAP2 affected your systems administration workload?

After an initial spin up period and extensive analysis of IT security implications, the system admin workload to maintain the system has been relatively minor, though not insignificant.� Mostly, the effort is in ensuring the OPeNDAP server capabilities are meeting user needs and are integrated with the rest of our distribution systems.

7. How well do the DAP2 systems scale to large numbers of simultaneous users, or to large datasets?
1. How much data does your DAP2 system handle in a typical month?

                                                               i.      Total data volume

                                                             ii.      Total number of data files

                                                            iii.      Percentage of data volume

                                                           iv.      Percentage of data files

Without an extensive analysis and estimation procedure, we cannot tell the volume of data served via OPeNDAP requests.� The �no parse header� aspect of the data serve loses information about the volume served I am told.� We could possibly estimate the volumes by looking at every log file entry and interpreting the OPeNDAP URL string to get a volume of data served, but this would be difficult.

8. Can you provide information on user statistics of your DAP2 systems?�
1. How many users does your DAP2 system handle in a typical month?

In 2004, we served approximately 100 distinct IP addresses per month through OPeNDAP.

                                                               i.      Total number of DAP2 users

In 2004, the total number was 1156.

                                                             ii.      Percentage of your overall users

Hard to say exactly, but for comparison we served via standard http 1642 unique IP addresses in 2004, and 145 via FTP.

2. Of the feedback you have received from your users on DAP2, what percentage is positive and what is negative?

We have received very little feedback other than from people within the data interoperability community, but what we have received has been all positive.

3. How have the user statistics changed over time?

I do not see any clear trends.� It appears that the number of OPeNDAP requests fluctuates a fair amount through 2004.