Making things run faster Post: 302248460

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Top Forums UNIX for Advanced & Expert Users Making things run faster Post 302248460 by shamrock on Friday 17th of October 2008 05:33:21 PM

10-17-2008

Registered User

Quote:

Originally Posted by Legend986

Added to that, I have a small question (not so sure if its silly though but can't seem to understand it completely)...

If I have four datasets like in the problem above and all I have to do is grep some text out of it, does it really make a difference doing the jobs parallely on all the datasets or doing them in a sequential order? In fact, to be more precise, the argument goes something like this:

Four datasets are stored on the disk. The CPU has to fetch some data everytime for the four processes to process them and write back to the disk. Now, if it has to provide data to all the four processes, then shouldn't the head keep moving around to provide the data as opposed to just one process where it just keeps reading the data (provided there is no fragmentation). As I said, I'm sorry if my question seems silly but just want to clear some basic concepts.

And that is the reason for caching data and striping it over multiple disks in order to reduce disk arm contention. This way reads/writes are done in parallel and with caching in play most reads/write are logical instead of physical. As you have terabytes of data I am assuming that all of it isn't on a single drive like a JBOD of some sort and that it is on a high end storage array with significant intelligence and caching built into it while being striped for performace and mirrored for availability.

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h5fromh4

H5FROMH4(1)							      h5utils							       H5FROMH4(1)

NAME

       h5fromh4 - convert HDF4 scientific datasets to an HDF5 file

SYNOPSIS

       h5fromh4 [OPTION]... [HDF4FILE]...

DESCRIPTION

       h5fromh4  takes one or more files in HDF4 format and outputs files in HDF5 format containing the datasets from the HDF4 files.  (Currently,
       only a single dataset per HDF4 file is converted.)

       HDF4 and HDF5 are free, portable binary formats and supporting libraries developed by the National Center for  Supercomputing  Applications
       at the University of Illinois in Urbana-Champaign.

       A  single  h5 file can contain multiple data sets; by default, h5fromh4 creates a dataset called "data", but this can be changed via the -d
       option, or by using the syntax HDF5FILE:DATASET with the -o option.  The -a option can be used to append new datasets to an  existing  HDF5
       file.   If the -o option is used and multiple HDF4 files are specified, all the HDF4 datasets are output into that HDF5 file with the input
       filenames (minus the ".hdf" suffix) used as the dataset names.

       The most basic usage is something like 'h5fromh4 foo.hdf', which will output a file foo.h5 containing the scientific dataset from foo.hdf.

OPTIONS

       -h     Display help on the command-line options and usage.

       -V     Print the version number and copyright info for h5fromh4.

       -v     Verbose output.

       -a     If the HDF5 output file already exists, append the data as a new dataset rather than overwriting the file  (the  default	behavior).
	      An existing dataset of the same name within the file is overwritten, however.

       -o file
	      Send  HDF5 output to file rather than to the input filename with .hdf replaced with .h5 (the default).  If multiple input files were
	      specified, this causes all input datasets to be stored in file (rather than in separate files), with the input filenames (minus  the
	      .hdf suffix) as the dataset names.

       -d name
	      Write  to  dataset  name	in  the  output; otherwise, the output dataset is called "data" by default.  Alternatively, use the syntax
	      HDF5FILE:DATASET with the -o option.

BUGS

       Send bug reports to S. G. Johnson, stevenj@alum.mit.edu.

AUTHORS

       Written by Steven G. Johnson.  Copyright (c) 2005 by the Massachusetts Institute of Technology.

h5utils 							   March 9, 2002						       H5FROMH4(1)