In this Document
A) You can create an ASM diskgroup using one of the following storage resources:
B) The procedures for preparing storage resources for ASM are:
C) Recommendations for Storage Preparation. The following are guidelines for preparing storage for
use with ASM:
This document describes how to prepare your storage sub-system before you configure Automatic Storage Management (ASM). When preparing your storage to use ASM, first determine the storage option for your system and then prepare the disk storage for the specific operating system environment.
1) Raw disk partition—A raw partition can be the entire disk drive or a section of a disk drive. However, the ASM disk cannot be in a partition that includes the partition table because the partition table can be overwritten.
2) Logical unit numbers (LUNs)—Using hardware RAID functionality to create LUNs is a recommended approach. Storage hardware RAID 0+1 or RAID5, and other RAID configurations, can be provided to ASM as ASM disks.
3) Raw logical volumes (LVM)—LVMs are supported in less complicated configurations where an LVM is mapped to a LUN, or an LVM uses disks or raw partitions. LVM configurations are not recommended by Oracle because they create a duplication of functionality. Oracle also does not recommended using LVMs for mirroring because ASM already provides mirroring.
4) NFS NAS files—If you have a certified NAS device, then you can create zero-padded files in an NFS mounted directory and use those files as disk devices in an Oracle Automatic Storage Management (Oracle ASM) diskgroup.
1) Configure two disk groups, one for the datafile and the other for the Flash Recovery Area. For availability purposes, one is used as a backup for the other.
2) Ensure that LUNs, which are disk drives of partitions, that ASM disk groups use have similar storage performance and availability characteristics. In storage configurations with mixed speed drives, such as 10K and 15K RPM, I/O distribution is constrained by the slowest speed drive.
3) Be aware that ASM data distribution policy is capacity-based. LUNs provided to ASM have the same capacity for each disk group to avoid an imbalance.
4) Use the storage array hardware RAID 1 mirroring protection when possible to reduce the mirroring overhead on the server. Use ASM mirroring redundancy in the absence of a hardware RAID, or when you need host-based volume management functionality, such as mirroring across storage systems. You can use ASM mirroring in configurations when mirroring between geographically-separated sites over a storage interface.
Hardware RAID 1 in some lower-cost storage products is inefficient and degrades the performance of the array. ASM redundancy delivers improved performance in lower-cost storage products.
5) Maximize the number of disks in a disk group for maximum data distribution and higher I/O bandwidth.
6) Create LUNs using the outside half of disk drives for higher performance. If possible, use small disks with the highest RPM.
7) Create large LUNs to reduce LUN management overhead.
8) Minimize I/O contention between ASM disks and other applications by dedicating disks to ASM disk groups for those disks that are not shared with other applications.
9) If you are using a high-end storage array that offers robust built-in RAID solutions, then Oracle recommends that you configure redundancy in the storage array by enabling RAID protection, such as RAID1 (mirroring) or RAID5 (striping plus parity). For example, to create an Oracle ASM disk group where redundancy is provided by the storage array, first create the RAID-protected logical unit numbers (LUNs) in the storage array, and then create the Oracle ASM disk group using the EXTERNAL REDUNDANCY clause.
10) Avoid using a Logical Volume Manager (LVM) because an LVM would be redundant. However, thereare situations where certain multipathing or third party cluster solutions require an LVM. In these situations, use the LVM to represent a single LUN without striping or mirroring to minimize the performance impact.
11) For Linux, when possible, use the Oracle ASMLIB feature to address device naming and permission persistency.
12) ASMLIB provides an alternative interface for the ASM-enabled kernel to discover and access block devices. ASMLIB provides storage and operating system vendors the opportunity to supply extended storage-related features. These features provide benefits such as improved performance and greater data integrity.
For Additional information please check the next manual:
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