Raw Devices on RHEL 5 or OEL 5

Be aware that raw device technology had been deprecated in RedHat Linux 5 (RHEL5) and Oracle Enterprise Linux 5 OEL5). / Linux Kernel 2.6
Does this mean we cannot use Rawdevices in RHEL5 or OEL5? As always there’s a workaround to make this happen by means of UDEV technique and Oracle 11g & 10gR2 has options to configure components to access the block devices directly instead of rawdevices.Before we jump into the workaround, let see what exactly is missing at the O/S level w.r.to rawdevices in RHEL5 and OEL5,

1. /etc/sysconfig/rawdevices file doesn’t exist
2. /dev/raw doesn’t exist.
3. Service by the name “rawdevices” doesn’t exist.

Trying to run the command “service rawdevices restart” will result in “rawdevices: unrecognized service”.

Now lets see an example of configuring rawdevices in RHEL4 and RHEL5.

RHEL4

To map a rawdevice to a block device /dev/sdf1

Step 1: Make an entry in /etc/sysconfig/rawdevices file

/dev/raw/raw1 /dev/sdf1

Step 2: For the mapping to have immediate effect, restart the rawdevices service.

$>service rawdevices restart

Step 3: Change ownership to oracle user

$>chown oracle:dba /dev/raw/raw1

RHEL5 / OEL5

Step 1: Make an entry in /etc/udev/rules.d/60-raw.rules or create your own file viz., /etc/udev/rules.d/<any_no_above_60>-oracle-raw.rules (eg. 63-oracle-raw.rules)

ACTION==”add”, KERNEL==”sdf1″, RUN+=”/bin/raw /dev/raw/raw1 %N”

Step 2: For the mapping to have immediate effect, run below command

$>/bin/raw /dev/raw/raw1 /dev/sdf1

So if you or your system administrator have plans to upgrade an existing release of RHEL or OEL to RHEL5 / OEL5 or planning to perform a new installation of RAC on RHEL5 / OEL5, wherein rawdevices will be / are used, please do take additional care.

For more information you can refer to following
Metalink notes

RAC FAQ: 220970.1 (look for “What storage option should I use for RAC 10g on Linux? ASM / OCFS / Raw Devices / Block Devices / Ext3 ?”)
How to map raw device on RHEL5 and OEL5 – Note 443996.1
Linux 2.6 Kernel Deprecation Of Raw Devices – Note:357492.1
How to install Oracle Clusterware with shared storage on block devices – Note:401132.1

Blogs / Forums
http://frits.homelinux.com/wordpress/?p=27 – Thanks to Frits Hoogland for sharing this information and also for the article on configuring 11g with ASM on CentOS on VMware.
http://www.webservertalk.com/archive221-2007-5-1884747.html – Thanks to Rupan for the explanation on Rawdevices and Block Devices.

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