Data Grids: Globus vs SRB

Maturity SRB  Older code base  Widely accepted across multiple communities  Core components are tightly integrated Globus  Data transfer components stable  Control, web service protocols are in flux  Optional value-added components have varying levels of stability

Interoperability SRB  Proprietary data and control protocol  Limited documentation available  Many language bindings Globus  Standards based protocols GGF Grid-ftp OGSI, WSRF  Common underlying communications protocol  Components are modular and can be mixed together in often arbitrary ways

Ease of use SRB  GUI and command line clients available  All developed clients must use provided tools  Simplified central administration Globus  Custom clients need to be designed.  Multiple entry points, so clients need not be aware of complete system  Each component has separate administration module

Cost SRB  Free software  Easy setup for simple installations  High cost to extend core functionality  Ease of developing clients through multiple tools  Ease of user access through supplied tools Globus  Free software  Complex setup of multiple disjoint components  Easier to extend core functionality using standard protocols  Clients may be complex due to multiple components  User access is up to grid developer Custom portals, registry services

Target Audiences SRB  Data access, preservation, management groups  Groups requiring ease of multiple datasets across administrative and technological boundaries  Limited to no internal data transformation requirements Globus  Computing and service based needs  Data components designed to feed into other services and usually not directly accessible to end users  Data exposed as a service

Support SRB  Single point of contact for support  Mailing lists, bug tracking, online manuals   Occasional tutorials at SDSC Globus  Multiple support groups depending on number of components used  From the Globus Alliance and the Globus community  Manuals, Mailing lists, online tutorials  Numerous seminars and tutorials around the world   Commercial support forthcoming (IBM, HP)

Component Comparison: Security SRB  Clear text passwords, GSI authentication  Central authorization  Complete separation between underlying operating system and SRB Globus  GSI authentication  Authorization depends on local sites and individual components Commonly just map GSI entities to local system users

Component Comparison: Data Access SRB  Srbmasters provide srb specific data moving protocol  MCAT tracks all available data holdings on srbmasters Tight coupling, all available data MUST be registered in MCAT Globus  Gridftp provides extended ftp services (striping, GSI authentication, etc)  Data locating handled through RLS Not tightly coupled to gridftp

Component Comparison: Data Discovery SRB  MCAT stores metadata system and descriptive centrally  Can be queried using SQL- like syntax  Database pass-throughs can be registered and directly queried with limited output transformation Globus  MCS can track limited descriptive metadata  OGSI-DAI can provide 3 rd party access to existing data sources  Not tightly coupled to underlying data on ftp services  Sepeaation between system and descriptive

Component Comparison: Processing SRB  Limited remote execution  Must be registered in MCAT and application installed on srbmaster  Cannot execute arbitrary code Globus  Easy to design add on services as web service  Can tie into existing compute resources  In hpc manner, many components can execute arbitrary jobs

Lessons Learned SRB  The SRB can easily handle textual metadata.  Extended metadata support requires extensive code modification  SRB needs to be treated as an end to end data grid and not as individual components Globus  Globus is flexible, but also complicated  Some Globus components are fragile (MCS, RFT) while others are very solid and reliable (GSI interfaces, GridFTP)  Globus is evolving and improving: the implementation was made much better with subsequent toolkit releases