02-17-2013
Hello Praveen,
I'm not sure if you are mixing FS layer and phisical (disk driver) layer. I was speaking about FS layer (and block device driver layer) in my first post.
mcnamara answer was right.
Quote:
Originally Posted by
Praveen_218
A block is still (on most FS) refers to 4K of data only.
On most system the page-cache is still of this fix sizes. Hence on all block I/O is of 4K or less. The file systems on such system utilizes the maximum size which is 4k.
However, if you see the disk architecture, they have been under trial by various vendors with various sector sizes; with 512bytes sector disk supported by most of the File system and storage product vendors (they however support various other size disks too -but 512b sector disk is in most common use probably because windows/DOS/UNIX FS supported them).
In order to support various disk architecture and FS supporting them use fragmentation which of course let you divide the 4k of page size into various fragments of 1, 2, ... 8 fragments per page.
8-fragments per page is the lowest value which translate into the size of a sector. You can of course not use a sector half of it. For I/O of 1 to full 512 byte of data a full sector gets used in one disk write.
Can you post here the steps you used to test this figures :
1) On UFS, how you saw the fragment size of 1 KB?
2) How did you looked at the 512kb I/O ?
1) fstype
2) dtrace script from DTrace Toolkit (bitesize.d)
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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)