How to Configure LUNs for ASM Disks using WWID, DM-Multipathing, and ASMLIB on RHEL 5/OL 5 and RHEL 6/OL 6
Last updated on SEPTEMBER 22, 2017
Applies to:Oracle Database - Enterprise Edition - Version 10.2.0.4 to 18.104.22.168 [Release 10.2 to 12.1]
This document details "how to" steps by using an example that creates devices for Automatic Storage Management (ASM) using World Wide Identifier (WWID), DM-Multipathing, and ASMLIB, utilizing a Hitachi Storage Sub-system. The simplified "how to" steps are for Red Hat Enterprise Linux version 5 (RHEL 5) and Oracle Linux version 5 (OL 5) on Linux x86-64 for preparing storage to use ASM.
Each multipath device has a World Wide Identifier (WWID), which is guaranteed to be globally unique and unchanging. By default, the name of a multipath device is set to its WWID. Alternately, you can set the user_friendly_names option in the multipath configuration file, which sets the alias to a node-unique name of the form mpathn. When the user_friendly_names configuration option is set to yes, the name of the multipath device is set to /dev/mpath/mpathn. Configuring multipathing by modifying the multipath configuration file, /etc/multipath.conf, will not be addressed in this document.
The WWID is a persistent, system-independent ID that the Small Computer Storage Interface (SCSI) Standard requires from all SCSI devices. Each disk attached to a Linux-based server has a unique SCSI ID. The WWID identifier is guaranteed to be unique for every storage device, and independent of the path that is used to access the device. This identifier can be obtained by issuing a SCSI Inquiry to retrieve the Device Identification Vital Product Data (page 0x83) or Unit Serial Number (page 0x80). The mappings from these WWIDs to the current /dev/sd names can be seen in the symlinks maintained in the /dev/disk/by-id/ directory.
In this document, the accessible disks are connected via a Host Bus Adapter Card (HBA) to a Storage Area Network (SAN) or switch. If the disks are attached via Hitachi SAN, the path and port information is also extracted. Disk arrays that are grouped together as Logical Unit Number (LUN) storage in SANs can also present themselves as SCSI devices on Linux servers. The command, "fdisk -l", lists attached SCSI disk devices, including those from a SAN. Multiple devices share common SCSI identifiers.
Automatic Storage Management Library (ASMLIB) driver is a support library for the Automatic Storage Management (ASM) feature of the Oracle Database and is available for the Linux operating system. This document discusses usage with Red Hat Enterprise Linux version 5 and Oracle Linux version 5.
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