How to determine OS block size for windows or unix 
In many times you probably have heard about set the oracle db block size as a multiple of the OS block size. But whenever you ask how I can determine or find OS block size for windows or Unix then many one get stopped. In fact this question is OS related. In this post I will show how I can get OS block.

1) UNIX or Linux System.
On my Solaris Machine,
SQL> !perl -e '$a=(stat ".")[11]; print $a'
8192

On my debian Linux,
$ perl -e '$a=(stat ".")[11]; print $a'
4096

On my Solaris Machine another way,
SQL> !df -g /oracle
/oracle (/dev/dsk/c1d0s3 ): 8192 block size 1024 frag size
Where /oracle is disk partition.

Another example,
SQL> !df -g | grep 'block size'
/ (/dev/dsk/c1d0s0 ): 8192 block size 1024 frag size
/devices (/devices ): 512 block size 512 frag size
/system/contract (ctfs ): 512 block size 512 frag size
/proc (proc ): 512 block size 512 frag size
/etc/mnttab (mnttab ): 512 block size 512 frag size
/etc/svc/volatile (swap ): 4096 block size 4096 frag size
/system/object (objfs ): 512 block size 512 frag size
/lib/libc.so.1 (/usr/lib/libc/libc_hwcap1.so.1): 8192 block size 1024 frag size
/dev/fd (fd ): 1024 block size 1024 frag size
/tmp (swap ): 4096 block size 4096 frag size
/var/run (swap ): 4096 block size 4096 frag size
/oradata1 (/dev/dsk/c1d0s4 ): 8192 block size 1024 frag size
/oracle (/dev/dsk/c1d0s3 ): 8192 block size 1024 frag size
/oradata2 (/dev/dsk/c1d0s5 ): 8192 block size 1024 frag size
/export/home (/dev/dsk/c1d0s7 ): 8192 block size 1024 frag size

2) Windows Machine.
If you use ntfs file system you can use
fsutil fsinfo ntfsinfo drivename: to get information of block size.

c:\>fsutil fsinfo ntfsinfo f:
NTFS Volume Serial Number : 0x1e345b64345b3e49
Version : 3.1
Number Sectors : 0x0000000004a852c0
Total Clusters : 0x0000000000950a58
Free Clusters : 0x00000000003ae433
Total Reserved : 0x0000000000000000
Bytes Per Sector : 512 
Bytes Per Cluster : 4096 -- This is OS block size.
Bytes Per FileRecord Segment : 1024
Clusters Per FileRecord Segment : 0
Mft Valid Data Length : 0x000000000d72a000
Mft Start Lcn : 0x00000000000c0000
Mft2 Start Lcn : 0x00000000004a812c
Mft Zone Start : 0x0000000000800720
Mft Zone End : 0x000000000083b920

To get All possible size on windows machine use,
c:\ format /? 
In the /A:size you will get the all possible size for both FAT and NTFS file system. Whenever you format a drive you can select default allocation unit as block size. 

3) On HPUX issue like "vgdisplay -v /dev/vg01/lvol"