Distributed data access in the sequential access model at the D0 experiment at Fermilab

PDF Version Also Available for Download.

Description

The authors present the Sequential Access Model (SAM), which is the data handling system for D0, one of two primary High Energy Experiments at Fermilab. During the next several years, the D0 experiment will store a total of about 1 PByte of data, including raw detector data and data processed at various levels. The design of SAM is not specific to the D0 experiment and carries few assumptions about the underlying mass storage level; its ideas are applicable to any sequential data access. By definition, in the sequential access mode a user application needs to process a stream of data, ... continued below

Physical Description

80 Kilobytes pages

Creation Information

Terekhov, Igor & White, Victoria July 5, 2000.

Context

This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided by UNT Libraries Government Documents Department to Digital Library, a digital repository hosted by the UNT Libraries. More information about this article can be viewed below.

Who

People and organizations associated with either the creation of this article or its content.

Publisher

Provided By

UNT Libraries Government Documents Department

Serving as both a federal and a state depository library, the UNT Libraries Government Documents Department maintains millions of items in a variety of formats. The department is a member of the FDLP Content Partnerships Program and an Affiliated Archive of the National Archives.

Contact Us

What

Descriptive information to help identify this article. Follow the links below to find similar items on the Digital Library.

Description

The authors present the Sequential Access Model (SAM), which is the data handling system for D0, one of two primary High Energy Experiments at Fermilab. During the next several years, the D0 experiment will store a total of about 1 PByte of data, including raw detector data and data processed at various levels. The design of SAM is not specific to the D0 experiment and carries few assumptions about the underlying mass storage level; its ideas are applicable to any sequential data access. By definition, in the sequential access mode a user application needs to process a stream of data, by accessing each data unit exactly once, the order of data units in the stream being irrelevant. The units of data are laid out sequentially in files. The adopted model allows for significant optimizations of system performance, decrease of user file latency and increase of overall throughput. In particular, caching is done with the knowledge of all the files needed in the near future, defined as all the files of the already running or submitted jobs. The bulk of the data is stored in files on tape in the mass storage system (MSS) called Enstore[2] and also developed at Fermilab. (The tape drives are served by an ADIC AML/2 Automated Tape Library). At any given time, SAM has a small fraction of the data cached on disk for processing. In the present paper, the authors discuss how data is delivered onto disk and how it is accessed by user applications. They will concentrate on data retrieval (consumption) from the MSS; when SAM is used for storing of data, the mechanisms are rather symmetrical. All of the data managed by SAM is cataloged in great detail in a relational database (ORACLE). The database also serves as the persistency mechanism for the SAM servers described in this paper. Any client or server in the SAM system which needs to store or retrieve information from the database does so through the interfaces of a CORBA-based database server. The users (physicists) use the database to define, based on physics selection criteria, datasets of their interest. Once the query is defined and resolved into a set of files, actual data processing, called a project, may begin. Obviously, running projects involves data transfer and resource management. The computing facilities with their CPU, disk, and other hardware resources are logically partitioned into collections of resources called stations. A station may be a single node, a fraction thereof (some of the machine's disks and/or CPUs may constitute a station) or a collection of smaller nodes. It is equipped with a server, called station master (SM), that coordinates data delivery and projects using the data. User requests to actually run a project proceed through the SM, which determines the amount of cache replacement, if any, needed to run the project. If viable, the user job is submitted into a station-associated batch queue, otherwise the project is rejected and the user may try another station.

Physical Description

80 Kilobytes pages

Source

  • Ninth IEEE International Symposium on High-Performance Distributed Computing, Pittsburgh, PA (US), 08/01/2000--08/04/2000

Language

Item Type

Identifier

Unique identifying numbers for this article in the Digital Library or other systems.

  • Report No.: FERMILAB-Conf-00/140-E
  • Grant Number: AC02-76CH03000
  • Office of Scientific & Technical Information Report Number: 757586
  • Archival Resource Key: ark:/67531/metadc703341

Collections

This article is part of the following collection of related materials.

Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

What responsibilities do I have when using this article?

When

Dates and time periods associated with this article.

Creation Date

  • July 5, 2000

Added to The UNT Digital Library

  • Sept. 12, 2015, 6:31 a.m.

Description Last Updated

  • April 1, 2016, 5:23 p.m.

Usage Statistics

When was this article last used?

Yesterday: 0
Past 30 days: 1
Total Uses: 5

Interact With This Article

Here are some suggestions for what to do next.

Start Reading

PDF Version Also Available for Download.

Citations, Rights, Re-Use

Terekhov, Igor & White, Victoria. Distributed data access in the sequential access model at the D0 experiment at Fermilab, article, July 5, 2000; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc703341/: accessed December 13, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.