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Top Forums UNIX for Advanced & Expert Users Physical disk IO size smaller than fragment block filesystem size ? Post 302768713 by rarino2 on Saturday 9th of February 2013 08:56:39 AM
Old 02-09-2013
Sun Physical disk IO size smaller than fragment block filesystem size ?

Hello,
in one default UFS filesystem we have 8K block size (bsize) and 1K fragmentsize (fsize). At this scenary I thought all "FileSytem IO" will be 8K (or greater) but never smaller than the fragment size (1K). If a UFS fragment/blocksize is allwasy several ADJACENTS sectors on disk (in a disk with sector=512B), all "physical disk IO" it will allways, like "Filesystem IO", greater than 1K.

But with dtrace script from DTrace Toolkit (bitesize.d) I can see IOs with 512B size.

¿What is wrong in my assumptions or what is the explanation?

Thank you very much in advance!!

Last edited by rarino2; 02-10-2013 at 08:43 AM..
 

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seeksize.d(1m)							   USER COMMANDS						    seeksize.d(1m)

NAME
seeksize.d - print disk event seek report. Uses DTrace. SYNOPSIS
seeksize.d DESCRIPTION
seeksize.d is a simple DTrace program to print a report of disk event seeks by process. This can be used to identify whether processes are accessing the disks in a "random" or "sequential" manner. Sequential is often desirable, indicated by mostly zero length seeks. Since this uses DTrace, only users with root privileges can run this command. EXAMPLES
Sample until Ctrl-C is hit then print report, # seeksize.d FIELDS
PID process ID CMD command and argument list value distance in disk blocks (sectors) count number of I/O operations DOCUMENTATION
See the DTraceToolkit for further documentation under the Docs directory. The DTraceToolkit docs may include full worked examples with ver- bose descriptions explaining the output. EXIT
seeksize.d will sample until Ctrl-C is hit. AUTHOR
Brendan Gregg [Sydney, Australia] SEE ALSO
iosnoop(1M), bitesize.d(1M), dtrace(1M) version 0.95 May 14, 2005 seeksize.d(1m)
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