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 NETBSD
diskpart
DISKPART(8) BSD System Manager's Manual DISKPART(8)
NAME
diskpart -- calculate default disk partition sizes
SYNOPSIS
diskpart [-d] [-p] [-s size] disk-type
DESCRIPTION
diskpart is used to calculate the disk partition sizes based on the default rules used at Berkeley.
Available options and operands:
-d An entry suitable for inclusion in the disk description file /etc/disktab is generated; for example, disktab(5).
-p Tables suitable for inclusion in a device driver are produced.
-s size The size of the disk may be limited to size with the -s option.
On disks that use bad144(8) type of bad-sector forwarding, space is normally left in the last partition on the disk for a bad sector forward-
ing table, although this space is not reflected in the tables produced. The space reserved is one track for the replicated copies of the ta-
ble and sufficient tracks to hold a pool of 126 sectors to which bad sectors are mapped. For more information, see bad144(8). The -s option
is intended for other controllers which reserve some space at the end of the disk for bad-sector replacements or other control areas, even if
not a multiple of cylinders.
The disk partition sizes are based on the total amount of space on the disk as given in the table below (all values are supplied in units of
sectors). The 'c' partition is, by convention, used to access the entire physical disk. The device driver tables include the space reserved
for the bad sector forwarding table in the 'c' partition; those used in the disktab and default formats exclude reserved tracks. In normal
operation, either the 'g' partition is used, or the 'd', 'e', and 'f' partitions are used. The 'g' and 'f' partitions are variable-sized,
occupying whatever space remains after allocation of the fixed sized partitions. If the disk is smaller than 20 Megabytes, then diskpart
aborts with the message ``disk too small, calculate by hand''.
Partition 20-60 MB 61-205 MB 206-355 MB 356+ MB
a 15884 15884 15884 15884
b 10032 33440 33440 66880
d 15884 15884 15884 15884
e unused 55936 55936 307200
h unused unused 291346 291346
If an unknown disk type is specified, diskpart will prompt for the required disk geometry information.
SEE ALSO
disktab(5), bad144(8)
HISTORY
The diskpart command appeared in 4.2BSD.
BUGS
Most default partition sizes are based on historical artifacts (like the RP06), and may result in unsatisfactory layouts.
When using the -d flag, alternative disk names are not included in the output.
BSD
June 6, 1993 BSD