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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LEARN ABOUT OSF1
disklabel
disklabel(4) Kernel Interfaces Manual disklabel(4)
NAME
disklabel - Disk pack label
SYNOPSIS
#include <sys/disklabel.h>
DESCRIPTION
Each disk or disk pack on a system may contain a disk label which provides detailed information about the geometry of the disk and the par-
titions into which the disk is divided. It should be initialized when the disk is formatted, and may be changed later with the disklabel
program. This information is used by the system disk driver and by the bootstrap program to determine how to program the drive and where
to find the file systems on the disk partitions. Additional information is used by the file system in order to use the disk most effi-
ciently and to locate important file system information. The description of each partition contains an identifier for the partition type
(standard file system, swap area, etc.). The file system updates the in-core copy of the label if it contains incomplete information about
the file system.
The label is located in sector number LABELSECTOR of the drive, usually sector 0 (zero) where it may be found without any information about
the disk geometry. It is at an offset LABELOFFSET from the beginning of the sector, to allow room for the initial bootstrap. The disk
sector containing the label is normally made read-only so that it is not accidentally overwritten by pack-to-pack copies or swap opera-
tions; the DIOCWLABEL ioctl, which is done as needed by the disklabel program, allows modification of the label sector.
A copy of the in-core label for a disk can be obtained with the DIOCGDINFO ioctl; this works with a file descriptor for a block or charac-
ter (raw) device for any partition of the disk. The in-core copy of the label is set by the DIOCSDINFO ioctl. The offset of a partition
cannot generally be changed, nor made smaller while it is open. One exception is that any change is allowed if no label was found on the
disk, and the driver was able to construct only a skeletal label without partition information. Finally, the DIOCWDINFO ioctl operation
sets the in-core label and then updates the on-disk label; there must be an existing label on the disk for this operation to succeed.
Thus, the initial label for a disk or disk pack must be installed by writing to the raw disk. All of these operations are normally done
using the disklabel program.
RELATED INFORMATION
Files: disktab(4)
Commands: disklabel(8) delim off
disklabel(4)