Using udev with Oracle Architecture (RAC & ASM) - Red Hat 4.0
(Doc ID 371814.1)
Last updated on DECEMBER 25, 2019
Applies to:
Oracle Database - Enterprise Edition - Version 10.2.0.1 to 10.2.0.2 [Release 10.2]Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Linux x86
Red Hat Enterprise Linux Advanced Server x86-64 (AMD Opteron Architecture)
Red Hat Enterprise Linux Advanced Server Itanium
Purpose
For Linux platforms the LUNs presented from a SAN, NAS or SCSI devices are identified with the path /dev/sdX. (/dev/sda, dev/sdb, etc). There is a common issue when disks are removed from the system (due to failures), changing the name.
Example: having /dev/sda, /dev/sdb, /dev/sdc, if disk /dev/sdb fails on the next reboot the system will discover /dev/sda and /dev/sdb, but /dev/sdb had the content originally referenced by /dev/sdc.
This is more a problem when using RAC environments. If the devices are bound to raw, it wont change because there is a static file (/etc/sysconfig/rawdevices or /etc/rc.local), where the bindind is executed. At the application level it could be a problem. For example, Oracle, will reference /dev/raw/raw2 for the OCR or Voting disk, but starting CRS will fail because of the content of the device is not the OCR or the voting disk.
Similar situation could apply to disks used by ASM where after the reboot the disk is not an ASM disk. ASMLIB is not a problem because it reads the content of the header and creates the block device under /dev/oracleasm/disks after finding the correct ASMLIB label.
The solution to avoid this type of situations is to guarantee consistent names for the devices through reboots. Linux 2.6 introduced udev as a mechanism to dynamically manage all type of devices, including disks.
This document presents details about how to configure udev and create persistent names and use these names in a RAC configuration, for OCR, Voting Disks and ASM disks.
Scope
The intended audience is people with general knowledge of configuring disks on Linux environments and RAC knowledge.
The hardware referenced in the document is a low end or low profile storage. As mentioned in the document, the number of partitions in the disks wont be appropiated for production environments.
Details
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