BaBar Data Distribution using the Storage Resource Broker

Adil Hasan, Wilko Kroeger (SLAC Computing Services),

Dominique Boutigny (LAPP),

Cristina Bulfon (INFN,Rome),

Jean-Yves Nief (ccin2p3),

Liliana Martin (Paris VI et VII),

Andreas Petzold (TUD),

Jim Cochran (ISU)

(on behalf of the BaBar Computing Group)

IX International Workshop on Advanced Computing and Analysis Techniques in Physics Research

KEK Japan

1-5 December 2003

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BaBar – the parameters (computing-wise)

• ~80 institutions in Europe and North America.• 5 Tier A computing centers:

– SLAC (USA), ccin2p3 (France), RAL (UK), GridKA (Germany), Padova (Italy).

• Processing of data done in Padova.• Bulk of simulation production done by remote

institutions.• BaBar computing is highly distributed.• Reliable data distribution essential to BaBar.

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The SRB• The Storage Resource Broker (SRB) is developed

by San Diego Supercomputing Center (SDSC).• A client-server middleware for connecting

heterogeneous data resources.• Provides a uniform method to access the resources.• Provides relational database backend to record file

metadata (metadata catalog called MCAT) and for access control lists (acls).

• Can use Grid Security Infrastructure (GSI) authentication.

• Also provides Audit information.

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The SRB

• SRB v3:– Define an SRB zone comprising of one MCAT and one

or more SRB servers. – Provides applications to federate zones (synch MCATs,

create users, data belonging to different zones).– Within one federation all SRB servers need to run on

the same port. – Allows an SRB server at one site to belong to more

than one zone.

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The SRB in BaBar

• The SRB feature-set makes it a useful tool for data distribution.

• Particle Physics Data Grid (PPDG) effort initiated interest in SRB.

• PPDG and BaBar collaboration effort has gone into testing and deploying the SRB in BaBar.

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The SRB in BaBar

• The BaBar system has 2 MCATs: one at SLAC and one at ccin2p3.

• Use SRB v3 to create and federate the two zones: SLAC and ccin2p3 zone.

• Advantage that client can connect to SLAC or ccin2p3 to see files at other site.

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The SRB in BaBar

MCAT enabled SRB serverSRB serverSRB clients

Data replicate from/copied toSLAC

Data copied fromSLAC

Data replicatefrom/copied toccin2p3

Data copied From ccin2p3

SLAC ccin2p3

SLAC Zone ccin2p3 Zone

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Data Distribution using SRB

• BaBar Data distribution with SRB consists of the following steps: – Publish files available for distribution in

MCAT (publication I).– Locate files to distribute (location).– Distribute files (distribution).– Publish distributed files (publication II).

• Each of these steps requires the user to belong to some ACL (authorization).

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Authorization• BaBarGrid currently uses European Data Grid

Virtual Organization (VO).– Consists of an Lightweight Directory Access Protocol

(LDAP) database holding certificate Distinguished Name (DN) strings for all BaBar members.

– Used to update Globus grid-mapfiles.

• SRB authentication akin to grid-mapfile:– Maps SRB username to DN string.– SRB username doesn’t have to map to UNIX username.

• Developing application to obtain user DN strings from VO.– App is experiment neutral.– Has ability to include information from Virtual

Organization Management System.9

Publication I

• The initial publication step (event store files) entails:– Publication of files into SRB MCAT once files have

been produced and published in BaBar bookkeeping.– Files are grouped into collections based on run range,

release, production type (SRB collection != BaBar collection).

– Extra metadata information (such as file UUID, BaBar collection name) stored in MCAT.

– SRB object name contains processing spec, etc that uniquely id the object.

– ~5K event files (or SRB objects) per SRB collection.

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Publication I

• Detector conditions files are more complicated as files are constantly updated (ie not closed).

• As files are update in SRB need to prevent users from taking an inconsistent copy.

• Unfortunately SRB does not currently permit locking of collections.

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Publication I

• Have devised a workaround:– Register conditions file objects under date-specified

collection.– Register a ‘locator file’ object containing the conditions

date-specified collection name.– Then, new conditions files registered under a new date-

specified collection.– ‘Locator file’ contents updated with new date-specified

collection.

• This method prevents users from taking an inconsistent set of files.

• Only two sets kept at any one time.

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Location & Distribution

• Location and distribution happen in one client application.

• User supplies BaBar collection name from BaBar bookkeeping.

• SRB searches MCAT for files that have that collection name as metadata.

• Files are then copied to target site.• SRB allows simple checksum to be performed.

– But checksum is not md5 or cksum.– Still can be useful.

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Location & Distribution

• SRB allows 3rd-party replication.– But, most likely we will always run distribution

command from source or target site.

• Also have the ability to create a logical resource of more than 1 physical resource.– Can replicate to all resources with one command.– Useful if more than 1 site regularly needs the data.

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Publication II

• Optionally can register copied file in MCAT (decision a matter of policy).

• Extra step for data distribution to ccin2p3: – Publication of files in ccin2p3 MCAT.– Required since current SRB v3 does not allow

replication across zones.

• Extra step not a problem since need to integrity check data before publishing anyway.

• Important note: data can be published & accessed at ccin2p3 or SLAC since MCATs will be synch’d regularly.

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SC2003 demonstration

• Demonstrated distribution of detector conditions files using scheme previously described to 5 sites:– SLAC, ccin2p3, Rome, Bristol, Iowa State.

• Data were distributed over 2 servers at SLAC and files were copied in a round-robin manner from each server.

• Files were continuously copied and deleted at target site.

• Demonstration ran 1 full week continuously without problems.

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SC2003 Demonstration

Rome Ccin2p3 ... Etc

SRB server

MCAT

Authenticate user Locate data

Request totransfer data

Request totransfer data

Transfer datato target

Transfer datato target

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SC 2003 demonstration18

Future work

• System currently being used, but not yet considered full production quality. Missing items:– SRB log file parser to automatically catch errors.– SRB server load monitor (cpu, memory).– Automatic generation of SRB .MdasEnv

and .MdasAuth files.– Automatic generation of new and deletion of old users

in MCAT.– Better packaging of client and server apps.– MCAT integrity checking scripts. – Better integration with BaBar Bookkeeping.

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Future work

• Slightly longer term:– Inclusion of management system to manage SRB

requests.• If system heavily used will require system to queue requests.• Currently looking at Stork to manage multiple requests

(http://www.cs.wisc.edu/condor/stork/).

– Interoperation with Replica Location Service (RLS) and Storage Resource Manager (SRM) (see Simon Metson’s talk).

• Allows integration with LCG tools.

– Move to grid-services.

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Summary• Extensive testing and interaction with SRB

developers has allowed BaBar to develop a data distribution system based on existing grid middle-ware.

• Used for distributing conditions files to 5 sites since October.

• Will be used to distribute: – Detector conditions files.

– Event store files.

– Random trigger files (used for simulation).

• BaBar’s data distribution system is sufficiently modular can be adapted to other environments.

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