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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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SCAN_FFS(8)						    BSD System Manager's Manual 					       SCAN_FFS(8)

NAME
scan_ffs, scan_lfs -- find FFSv1/FFSv2/LFS partitions on a disk or file SYNOPSIS
scan_ffs [-blv] [-e end] [-F file] [-s start] device DESCRIPTION
scan_ffs will take a raw disk device that covers the whole disk or a file and will find all possible FFSv[12]/LFS partitions, independent of block sizes on it. It will show the file system type (FFSv1, FFSv2, or LFS), size, and offset. Also it has an option to show the values with a disklabel-alike output. The options are as follows: -b Report every superblock found with its sector address, rather than trying to report the partition boundaries. This option can be useful to find the other superblocks in a partition if the first superblock has become corrupted. It is most useful if device refers to the raw device for the partition, rather than the entire disk. -e end Where to stop searching for file systems. The end argument specifies the last sector that will be searched. Default is the last sector of device. -F file Path to a file containing possible partitions inside of it. -l Print out a string looking much like the input to disklabel. With a little massaging, this output can usually be used by disklabel(8). -s start Where to start searching for file systems. This makes it easier to skip swap partitions or other large non-UFS/FFS partitions. The start argument specifies the first sector that will be searched. Default is the first sector of device. -v Be verbose about what scan_ffs is doing, and what has been found. The device argument specifies which device scan_ffs should scan for file systems. scan_lfs is just another name for the same program, both behave in exactly the same way. SEE ALSO
disklabel(8) HISTORY
The scan_ffs program first appeared in OpenBSD 2.3 and then in NetBSD 3.1. Support for searching in files was added in NetBSD 4.0. AUTHORS
scan_ffs was written for OpenBSD by Niklas Hallqvist and Tobias Weingartner. It was ported to NetBSD by Juan Romero Pardines, who added sup- port for LFS/FFSv2, partitions with fragsize/blocksize greater than 2048/16384 for FFSv1, searching on files, etc. BUGS
Currently scan_ffs won't find partitions with fragsize/blocksize greater than 8192/65536. BSD
May 1, 2007 BSD
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