Recommendations for Storage Preparation

The following are guidelines for preparing storage for use with Oracle ASM:

  • Configure two disk groups, one for data and the other for the fast recovery area.

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  • The number of LUNs (Oracle ASM disks) for each disk group should be at least equal to four times the number of active I/O paths. For example, if a disk group has two active I/O paths, then minimum of eight LUNs should be used. The LUNs should be of equal size and performance for each disk group.

    An I/O path is a distinct channel or connection between storage presenting LUNs and the server. An active I/O path is an I/O path in which the I/O load on a LUN is multiplexed through multipathing software.

  • Ensure that all Oracle ASM disks in a disk group have similar storage performance and availability characteristics. In storage configurations with mixed speed drives, such as flash memory and hard disk drives (HDD), I/O performance is constrained by the slowest speed drive.

  • Oracle ASM data distribution policy is capacity-based. Ensure that Oracle ASM disks in a disk group have the same capacity to maintain balance.

  • Configure a minimum of three failure groups for normal redundancy disk groups and five failure groups for high redundancy disk groups to maintain the necessary number of copies of the Partner Status Table (PST) to ensure robustness with respect to storage hardware failures. For more information, refer to "Oracle ASM Failure Groups".

  • Create external redundancy disk groups when using high-end storage arrays. High-end storage arrays generally provide hardware RAID protection. Use Oracle ASM mirroring redundancy when not using hardware RAID, or when you need host-based volume management functionality, such as mirroring across storage systems. You can use Oracle ASM mirroring in configurations when mirroring between geographically-separated sites (extended clusters).

  • Minimize I/O contention between Oracle ASM disks and other applications by dedicating disks in Oracle ASM disk groups.

  • Choose a hardware RAID stripe size that is a power of 2 and less than or equal to the size of the Oracle ASM allocation unit.

  • Use the Oracle ASM Filter Driver feature to provide consistent device naming and permission persistency.

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