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Parallel I/O

Parallel I/O. A. Patra MAE 609/CE667. What is Parallel I/O ?. Parallel processes need parallel input/output Ideal: Processor consuming/producing data reads/writes it directly Not practical for large numbers of processors. What is Parallel I/O ?. What is Parallel I/O ?. R. Lusk :

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Parallel I/O

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  1. Parallel I/O A. Patra MAE 609/CE667 ...

  2. What is Parallel I/O ? • Parallel processes need parallel input/output • Ideal: Processor consuming/producing data reads/writes it directly • Not practical for large numbers of processors ...

  3. What is Parallel I/O ?

  4. What is Parallel I/O ? • R. Lusk : • Multiple Processes Participate in the I/O • Application level parallelism • “File” is stored on multiple disks on a parallel file system • Additional Interfaces for I/O

  5. What is Parallel I/O ? • File is stored on multiple disks on a parallel file system

  6. What is Parallel I/O ? • I/O should be parallel at both ends • Application program end -- with access to single logical file that is distributed across physical disks • I/O should be physically parallel so that parallel performance scales with no. of processors etc.

  7. Parallel File Systems • Provide users with • a consistent name space across the machine, • aids programmers in accessing file data on multiple nodes • physical distribution of data across disks and network entities, and, • eliminates bottlenecks both at the disk interface and the network, providing more effective bandwidth to the I/O resources

  8. Parallel File Systems • Example Systems • PFS -- Intel Paragon • XFS -- SGI Origin • PIOFS-- IBM SP • PVFS -- Linux cluster

  9. Parallel Virtual File System(PVFS) • PVFS system consists of three components: • the manager daemon, which runs on a single node, • handles permission checking for file creation, open, close, and remove operations • the I/O daemons, one of which runs on each I/O nodes, and handle all file I/O • application library, through which applications communicate with the PVFS daemons.

  10. Parallel Virtual File System(PVFS) • File striping • File partitioning • Application-oriented interfaces • Operation with existing binaries When using PVFS, nodes who perform computation (compute nodes) must communicate with nodes who perform I/O operations (I/O nodes) in order for file system operations to take place. Application tasks use one of the interfaces available in the PVFS libraries to communicate with the I/O daemons, who use UNIX read() and write() calls to perform I/O operations on the local disks

  11. PVFS • small data transfers tend to lead to very poor throughput. • Streams-based approach to data transfer is an attempt to improve overall network throughput by: • reducing the number of control messages • removing stripe and partition dependence on message sizes

  12. PVFS I/O stream between an application and an I/O node resulting from a strided request. Each side calculates the intersection of physical stripe and the strided request. The data is always passed in ascending byte order and is packed into TCP packets by the underlying networking software.

  13. PIOFS -- IBM An RS/6000 SP with several client nodes accessing data at server nodes. The Parallel I/O File System supports simultaneous access of server nodes by multiple client nodes.

  14. PIOFS -- IBM • PIOFS lets you create files as large as 128 Terabytes that span multiple server nodes. • With PIOFS file partitioning, you can parallelize access to your data without the inconvenience and administrative overhead of maintaining multiple data files. • PIOFS files can be dynamically partitioned into subfiles many different ways, all without altering or moving the contents of the file. • PIOFS supports parallelism in two complementary ways: physically and logically: • A file can be divided physically over multiple disks and servers. • A file can be divided logically into multiple subfiles.

  15. File Partitioning 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 . . . . . . . . . . . . . . file with numbers File split into 8 subfiles by columns

  16. File Partitioning • File split into 8 subfiles by rows • File split in 3 with wrapping

  17. Matrix-Matrix Multiply Tasks 0 and 1 process the first N/2 rows of matrix A Tasks 2 and 3 process the last N/2 rows of matrix A Tasks 0 and 2 process the first N/2 columns of matrix B Tasks 1 and 3 process the last N/2 columns of matrix B

  18. Parallel I/O is active research Only 1 complete MPI-IO implementation available Picture will stabilize over the next few years (1-2)

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