Installation guide

4. Optionally you can assign aliases in multipaths section. The value of WWID can be obtained with

scsi_id utility. For example:

# scsi_id -g -u -s /block/sda

In Oracle RAC, the clusterware device names must be persistent across reboots. The aliases can help to

create human friendly persistent named for the OCR (primary and mirror) disks, CSS voting disks and

also for ASM disks (if using ASM without ASMLib).

5. Perform a multipath dry run and evaluate the setup by running the following command.

# multipath -v2 -d

6. If the listing is appropriate, commit the configuration as follows:

a. Start multipath daemon

# service multipathd start

b. Execute the multipath command:

# multipath -v2

7. To get a listing of the current setup do:

# multipath -ll

8. Integrate the startup of the appropriate daemons in the boot sequence as follows:

# chkconfig --add multipathd

# chkconfig multipathd on

The device mapper creates kernel block devices (/dev/dm-*) and block devices with persistent names in the

/dev/mapper directory. The Red Hat Enterprise Linux 5 udev facility reacts to the event of creating a new /

dev/dm-* device by executing rules specified in /etc/udev/rules.d/40-multipath.rules. In par-

ticular, it creates symlinks under /dev/mpath directory pointing to the /dev/dm-* name.

Optimization of Disk Partitions on RAID

Storage arrays usually stripe data across several physical disk drives in large chunks, typically 64KB in size.

Aligning partitions to these stripe sizes can improve performance, particularly with database servers using direct

I/O.

Red Hat Enterprise Linux 5 contains two utilities that can be used to create disk partitions: fdisk and part-

ed. To ensure maximum compatibility with other operating systems, fdisk creates partitions that are aligned

to cylinder boundaries using the legacy cylinder/head/sector (C/H/S) geometry. Usually this geometry is not

aligned to the stripes in a RAID array. If a RAID volume is only going to be accessed by operating systems and

utilities that fully support Logical Block Addressing (LBA), then C/H/S alignment is not necessary and stripe

alignment can be created with the parted tool.

36 | www.redhat.com