Oxford Jan 2005 RAL Computing 1 RAL Computing Implementing the computing model: SAM and the Grid Nick West.
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Oxford Jan 2005 RAL Computing 1 RAL Computing Implementing the computing model: SAM and the Grid Nick West
Oxford Jan 2005 RAL Computing 2 An aside – do we want another email list? Currently all RAL software changes –Get reported to:- firstname.lastname@example.org@listserv.rl.ac.uk Are people happy with this spam? –Or should we have a separate list dealing specifically with technical computing issues?
Oxford Jan 2005 RAL Computing 3 Sam at RAL SAM (Sequential data Access with Metadata) –Tracks and records metadata at file and dataset level –Delivers files through a range of protocols e.g. D’cache. SAM at Remotes sites –Inefficient to repeatedly retrieve data from FNAL ENSTORE –Solution: SAM Station with local cache Optimisation to use local copy where present Local copy remains until clients release
Oxford Jan 2005 RAL Computing 4 Sam at RAL DCM (Data Cache Manager) v. SAM –DCM designed (from initial request by Alfons) to Allow sharing of a pool of data files Provide simple retrieval system from FNAL –Using MySQL query to infer directory from run number –Then wget or FTP to retrieve –Overlap functionality with SAM DCM advantages –Better disk management: audits all files by user –Simple interface (directory of soft links) for one-off jobs –Potential for expansion to crib Jeff’s use of COMPLETE_FILE_LISTING SAM advantages –Better catalogue of file locations – will track future changes –Support for datasets – formation and tracking
Oxford Jan 2005 RAL Computing 5 Sam at RAL Hybrid Proposal: DCM over SAM –Rather than SAM station use SAM web client (already installed at RAL and Oxford) –It provides full database functionality without a local cache. –Advantage of minimal coupling to SAM – just some python scripts + web interface
Oxford Jan 2005 RAL Computing 6 The Grid What is the Grid? –A set of tools and protocols allowing secure distributed computing over a heterogeneous distributed computing community. Why have a Grid? –To handle projects that require more resources than a single centre can provide. In HEP specifically LHC. How is it managed? –Groups are organised into VOs (Virtual Organisations) –Individuals are identified by GRID Certificates and then join VOs. Why do we care? –After all we only want a small slice of one site. –Because RAL will move all its resources over to the GRID They don’t want to have to maintain two systems Expect to be GRID-only by end of 2006
Oxford Jan 2005 RAL Computing 7 The Grid How will it impact us? –The original model mandated:- No external connectivity –Parcel up software + data and send to worker node. All data access via GRID tools e.g. SRM (Storage Resource Manager) –Potentially it could be very serious Database access ? –In principle would mean programming to another API and breaking our DB support libraries SAM access? –Requires web access Event data access? –Currently homogenous farm all nodes share the same disks –That's not the GRID model: each node only has local disks
Oxford Jan 2005 RAL Computing 8 The Grid Database Access: Exploiting cracks in the model –Already arguments between groups and system managers over issues such as databases. –Solution: exceptions to the model are “VO Boxes” that contain non-grid software. –I think the MySQL database at RAL is one such box. Taking “Distributed” out of Distributed Computing –To use RAL’s MySQL must run at RAL –The GRID has access to a set of CEs (Computing Elements) –RAL is only one CE – jobs could run elsewhere –But can target jobs to specific CE
Oxford Jan 2005 RAL Computing 9 The Grid SAM access –It looks like web access will be allowed Data Access –Probably won’t be able to do an end-run round GRID –Perhaps then have to use SAM – The SAMGrid project? –Need to talk to the guys at RAL, particularly Steve Traylen system manager for RAL CE.
Oxford Jan 2005 RAL Computing 10 The Grid What Grid Tools? –Larger experiments have posts dedicated to integrating experiments production systems into the GRID GridPP Portal Project –To support small experiments –Contact: Gidon Moont Imperial College –Already used by projects such as CALICE (Linear Collider calorimetry R&D) and MICE. –He is keen to help us when we are ready. It’s not all LHC –Older experiments e.g. ZEUS and H1 are already exploiting it. It could be worth looking at what they have done.
Oxford Jan 2005 RAL Computing 11 The Grid Our next steps –Mike is planning to talk to some experts (I think) –We need to talk to Steve Traylen about satisfying our requirements at RAL Gidon Moont about a Portal Project –Establish a VO and get some GRID certificates –Have some trial runs to identify and eliminate problems ahead of any forced migration.