LUN management at the heart of SAN configuration.
Disk drives are the foundation of modern data storage, but operating systems cannot use physical storage directly. The platters, heads, tracks and sectors of a physical drive must be translated into a logical space that an operating system sees as a linear address space comprised of fixed-size blocks. This translation process creates a logical entity that allows operating systems to read/write files. Storage networks must also partition their physical disks into logical entities so that host servers can access storage area network (SAN) storage, and each logical portion is called a logical unit number (LUN). This article explains essential LUN concepts and the role of LUNs in SAN technology.
What is LUN?
If suppose we got a large storage array, and requirement is to not allow one server to use all storage spaces, so it need to divided into logical units as LUN(Logical Unit Number). So LUN allow us slice storage array into usable storage chunks and present same to server. LUN basically refer to either a entire physical volume or subset of larger physical disk or volume. LUN represent logical abstraction or you can say virtual layer between physical disk and application. A LUN is scsi concept.
Preparing Disks for ASM
You can create an ASM disk group using one of the following storage resources:
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.
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.
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.
NFS files—ASM supports NFS files as ASM disks. Oracle Database has built-in support for the network file system (NFS) and does not depend on OS support for NFS. Although NFS and ASM have overlapping functionality, ASM can load balance or mirror across NFS files.
The procedures for preparing storage resources for ASM are:
Identify or create the storage devices for ASM by identifying all of the storage resource device names that you can use to create an ASM disk group. For example, on Linux systems, device names are typically presented from the /dev directory with the /dev/device_name_identifier name syntax.
Change the ownership and the permissions on storage device resources. For example, the following steps are required on Linux systems:
Change the user and group ownership of devices to oracle:dba
Change the device permissions to read/write
On older Linux versions, you must configure raw device binding
After you have configured ASM, ensure that disk discovery has been configured correctly by setting the ASM_DISKSTRING initialization parameter.
Disk drives are the foundation of modern data storage, but operating systems cannot use physical storage directly. The platters, heads, tracks and sectors of a physical drive must be translated into a logical space that an operating system sees as a linear address space comprised of fixed-size blocks. This translation process creates a logical entity that allows operating systems to read/write files. Storage networks must also partition their physical disks into logical entities so that host servers can access storage area network (SAN) storage, and each logical portion is called a logical unit number (LUN). This article explains essential LUN concepts and the role of LUNs in SAN technology.
What is LUN?
If suppose we got a large storage array, and requirement is to not allow one server to use all storage spaces, so it need to divided into logical units as LUN(Logical Unit Number). So LUN allow us slice storage array into usable storage chunks and present same to server. LUN basically refer to either a entire physical volume or subset of larger physical disk or volume. LUN represent logical abstraction or you can say virtual layer between physical disk and application. A LUN is scsi concept.
Preparing Disks for ASM
You can create an ASM disk group using one of the following storage resources:
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.
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.
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.
NFS files—ASM supports NFS files as ASM disks. Oracle Database has built-in support for the network file system (NFS) and does not depend on OS support for NFS. Although NFS and ASM have overlapping functionality, ASM can load balance or mirror across NFS files.
The procedures for preparing storage resources for ASM are:
Identify or create the storage devices for ASM by identifying all of the storage resource device names that you can use to create an ASM disk group. For example, on Linux systems, device names are typically presented from the /dev directory with the /dev/device_name_identifier name syntax.
Change the ownership and the permissions on storage device resources. For example, the following steps are required on Linux systems:
Change the user and group ownership of devices to oracle:dba
Change the device permissions to read/write
On older Linux versions, you must configure raw device binding
After you have configured ASM, ensure that disk discovery has been configured correctly by setting the ASM_DISKSTRING initialization parameter.
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