Raw Devices

Create a raw device from a file
#create an empty file
dd if=/dev/zero of=/oradata/al12/DATA/asmdisk/disk1 bs=1M count=125

#as root
losetup /dev/loop1 /oradata/al12/DATA/asmdisk/disk1
#check the raw device (untested)
losetup /dev/loop1 

[/etc/sysconfig/rawdevices]
/dev/raw/raw1 /dev/loop1

#restart raw device service
service rawdevices restart

#change ownership on raw device
chown oracle:dba /dev/raw/raw1

#if you change the size of the file directly using dd, then you must restart the service

Creating partitions
fdisk -l
Disk /dev/hda: 8589 MB, 8589934592 bytes
15 heads, 63 sectors/track, 17753 cylinders
Units = cylinders of 945 * 512 = 483840 bytes

Disk /dev/hda doesn't contain a valid partition table

fdisk /dev/hda
n, p, 1, 1(or more to skip initial blocks), +250M

This file contains the list of raw devices
[/etc/sysconfig/rawdevices]
/dev/raw/raw6   /dev/hda1
/dev/raw/raw7   /dev/hdb1

Service
service rawdevices restart

Format the partion
dd if=/dev/zero of=/dev/raw/raw1 bs=1M count=125

Oracle & Raw devices
Size of Redo Log = Raw Partition Size - 1*512 byte block
Size of Data File = Raw Partition Size - 2* Oracle Block Size