Database Reference
In-Depth Information
Figure 5-5. iSCSI storage configuration for a two-node RAC
Multipath Device Configuration
It is a recommended best practice to configure redundant I/O paths between Oracle RAC servers and storage, to
ensure high availability of shared storage access, as shown in the figures in the last section. For example, from RAC
host1, there are four redundant I/O paths to a same storage volume. These redundant I/O paths are represented by
multiple SCSI devices on the RAC node that point to the same storage volume (also called logical unit, identified by
the LUN). Since these SCSI devices are pointing to the same LUN, they have the same SCSI ID.
For example, /dev/sdc and /dev/sde represent two redundant I/O paths to the same LUN with the scsi ID:
36842b2b000742679000007a8500b2087. You can use the scsi_ID command to find the SCSI ID of a device:
[root@k2r720n1 $scsi_id /dev/sdc
36842b2b000742679000007a8500b2087
The following Linux shell script finds the SCSI IDs of the devices:
[root@k2r720n1 ~]# for i in sdc sdd sde sdf ; do printf "%s %s\n" "$i" "$(scsi_id --page=0x83
--whitelisted --device=/dev/$i)"; done
sdc 36842b2b000742679000007a8500b2087
sdd 36842b2b000742679000007a5500b1cd9
sde 36842b2b000742679000007a8500b2087
sdf 36842b2b000742679000007a5500b1cd9
Many OS have their own multipathing software that can be used to create a pseudo-device to facilitate the
sharing and balancing of I/O operations of LUNs across all available I/O paths. For example in Linux, a commonly
used multipath device driver is the Linux native Device Mapper. To verify whether or not the rpm package is already
installed, you can run this command:
[root@k2r720n1 yum.repos.d]# rpm -qa | grep device-mapper-multipath
device-mapper-multipath-libs-0.4.9-56.el6_3.1.x86_64
device-mapper-multipath-0.4.9-56.el6_3.1.x86_64
If the rpm package is not installed by default, you can install it from the yum repository:
$yum -y install device-mapper-multipath
 
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