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DD command using block device as input
Post 302666061 by Corona688 on Tuesday 3rd of July 2012 03:43:10 PM
07-03-2012
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So far with my tests I find that reading 16kb takes about the same time as reading 512b.
Too bad there isn't a tool which can tell you more about what your disk's doing, test uncached reads, or even configure hardware read-ahead to your preference... something like hdparm...
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I need this information to set the optimal page size of my system (oracle and mysql suggest these sizes)
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Can you elaborate on why dropping the caches is a bad idea?
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How about this sudo procedure:
- drop_caches
- flush disk-cache with hdparm
- make sure dd is in memory
- position the read head randomly on disk
- with DD: read X amount of bytes from the beginning of my file (this is timed)
- drop_caches
- flush disk-cache with hdparm
- make sure dd is in memory
- position the read head randomly on disk
- with DD: read X amount of bytes from the beginning of my file (this is timed)
Last edited by Corona688; 07-03-2012 at 04:51 PM..
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LEARN ABOUT OPENDARWIN
lessecho
LESSECHO(1) General Commands Manual LESSECHO(1) NAME
lessecho - expand metacharacters, such as * and ?, in filenames on Unix systems. SYNOPSIS
lessecho [-ox] [-cx] [-pn] [-dn] [-a] file ... DESCRIPTION
This manual page documents briefly the lessecho command. This manual page was written for the Debian GNU/Linux distribution because the original program does not have a manual page. lessecho is a program that simply echos its filename arguments on standard output. But any argument containing spaces is enclosed in quotes. OPTIONS
A summary of options are included below. -ox Specifies "x" to be the open quote character. -cx Specifies "x" to be the close quote character. -pn Specifies "n" to be the open quote character, as an integer. -dn Specifies "n" to be the close quote character, as an integer. -a Specifies that all arguments are to be quoted. The default is that only arguments containing spaces are quoted. SEE ALSO
less(1) AUTHOR
This manual page was written by Thomas Schoepf <schoepf@debian.org>, for the Debian GNU/Linux system (but may be used by others). Less was written by Mark Nudelman <markn@greenwoodsoftware.com> LESSECHO(1)