02-09-2013
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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newfs(8) System Manager's Manual newfs(8)
Name
newfs - construct a new file system
Syntax
/etc/newfs [ -N ] [ -n ] [ -v ] [ mkfs-options ] special disk-type
Description
The command is a front-end to the program. The program looks up the type of disk a file system is being created on in the disk description
file calculates the appropriate parameters to use in calling then builds the file system by forking If the file system is a root partition,
installs the necessary bootstrap program in the initial 16 sectors of the device.
If there is no disk description for the specified disk type in the file, the program will use the subroutine to derive disk geometry infor-
mation from the controlling device driver. This functionality is provided for MSCP and SCSI disks.
Options
-N Runs in no update mode. In this mode, will not write to
-n Prevents the bootstrap program from being installed.
-v Instructs to print out its actions, including the parameters passed to
Options which may be used to override default parameters passed to are:
-s size The size of the file system in sectors.
-b block-size
The block size of the file system in bytes.
-f frag-size
The fragment size of the file system in bytes.
-t #tracks/cylinder
-c #cylinders/group
The number of cylinders per cylinder group in a file system. The default value used is 16.
-m free space %
The percentage of space reserved from normal users; the minimum free space threshold. The default value used is 10%.
-o optimization
Specifies whether the file system will optimize for space or for time.
-r revolutions/minute
The speed of the disk in revolutions per minute (normally 3600).
-S sector-size
The size of a sector in bytes (almost never anything but 512).
-i number of bytes per inode
This specifies the density of inodes in the file system. The default is to create an inode for each 2048 bytes of data space.
If fewer inodes are desired, a larger number should be used; to create more inodes a smaller number should be given.
Files
For disk geometry and file system partition information
To actually build the file system
For boot strapping program
See Also
disktab(5), fs(5), chpt(8), fsck(8), format(8v), creatediskbyname(3x), mkfs(8), tunefs(8)
"A Fast File System for UNIX", Supplementary Documents, Volume 3: System Manager
newfs(8)