Oracle Database Tips by Donald Burleson

Oracle10g Grid Computing with RAC
Chapter 5 - Preparing Shared Storage

Storage Control Layer (SCL) Role

One of the main objectives of the SCL module is to physically disable the SAN storage whenever the server drops out of the matrix or cluster membership. Thus, it can perform I/O fencing. I/O fencing ensures integrity within the cluster by excluding rogue nodes from accessing critical data.

MxS features true I/O fencing (i.e., port disabling at the FC switch), which allows an administrator to log in to the ejected node, diagnose and repair the problem before restarting, and allowing an ejected server to rejoin the cluster.

Matrix Server provides each disk with a globally unique device name that all servers in the Matrix can use to access the device. When a SAN disk is imported into the matrix, a name prefixed by psd is assigned, e.g. psd1, psd2, and psd12. Individual disk partitions also have a global device name. It has the name and partition number. For example, partition 5 of disk 'psd14' is represented as psd14p5. On each server, Matrix Server creates device node entries in the directory /dev/psd for every partition on the disk. The SCL stores the device name and physical UID for each imported disk device in an internal database. This database resides on a membership partition that is assigned at the time of MxS installation.