It is recommended that you:
- Create all ASM disk groups with external redundancy (no mirroring), except for OCR and the voting disk (which use normal redundancy). The OCR disk group does not contain user data and remains small. When set to normal redundancy, Oracle creates three quorum files rather than one (as in external redundancy). Having three quorum files helps to avoid delays while the nodes try to register with the quorum during a high database activity.
- Use UDEV rules so that the device IDs are used in a persistent manner to set permissions and accessible aliases. The UDEV rules identify the disks by using a unique WWN for each device to create a symbolic link and associate permissions to the device that is persistent across the reboots. Aliases and permissions are often set differently by different customers. The following examples show a sample configuration file with UDEV rules.
- The following example shows a sample udev format:
##OCR disk information
KERNEL=="scini*", OPTIONS:="nowatch", SUBSYSTEM=="block", PROGRAM="/lib/udev/scsi_id --page=0x83 --whitelisted --device=/dev/%k", RESULT=="22c90f6da354e6d0f693faf2a0000001b", SYMLINK+="oracleasm/ocrvote1", OWNER="grid", GROUP="asmadmin", MODE="0660"
- An alternative udev format for rules, is:
/lib/udev/scsi_id -g -u -d /dev/sdb
# cd /etc/udev/rules.d/
# vi 99-oracle-asmdevices.rules
KERNEL=="sd*1", OPTIONS:="nowatch", SUBSYSTEM=="block", PROGRAM=="/usr/lib/udev/scsi_id -g -u -d /dev/$parent", RESULT=="360000970000196800312533030344131", SYMLINK+="ora-data1", OWNER="oracle", GROUP="oracle", MODE="0660"
# udevadm control --reload-rules && udevadm trigger
- Avoid placing the redo log files in the OCR and voting disk groups and create separate disk groups for OCR, REDO, DATA, and FRA.
- To avoid excessive redo log switches, create each database instance with redo log files of sufficient size. In the performance tests, each redo log group is sized at 50 GB.
- Create sufficient redo log groups for each instance so that the database archive log process has enough time to process each log before it becomes active again.
- Run the following command to set the Oracle redo logs to a fine-grained striping of 128 KB.
SQL> ALTER DISKGROUP <redo log ASM diskgroup_name> ALTER TEMPLATE onlinelog ATTRIBUTES (FINE);
- Ensure that enough free disk space exists in the Undo tablespace for maintaining the undo records.