ORACLE AUTOMATIC STORAGE Management Translator-tenth ASM built-in data structure (3) End

Disk Directory

Disk directory contains information about all the disks in the disk group. Disk directory information is more detailed than PST. Each disc in a disk group has an entry that is indexed by a number. The file number of disk directory is number 2nd (F2) in each disk group.

The fields in Disk directory are as follows:

N Disk Name

N Failure Group Name

n Disk Size

n Disk Free Space

n Disk creation time

Most of the information in disk directory is available in the disk header. Alterdiskgroup ... The check command verifies the consistency of the data structures on the disk. Diskdirectory is always available when the disk group is mount, so he also provides disk information about offline disk groups in normal-or high-redundancy mode.

Active Change Directory (ACD)

ACD is a log structure that allows ASM to record changes to multiple metadata structures. Redo LOG similar to Oracle RDBMS. Each instance has a 42M size chunk ACD. (as Douglas Adams explains in Hitchhiker ' Sguide to the Galaxy, the answer to the ultimate question of life is "42", the Universe and everything.) The first block of each chunk contains the Open/close state and checkpoint. The checkpoint is updated every 3 seconds. The remainder of the block is used to save the ACD modification record of the loop buffer. (Yes, "Active change Directory change record" is redundant, but there is no second modification, we cannot call it a ACDC record). The new ASM instance ACD will grow dynamically as needed. ASM uses ACD to perform crash recovery and instance recovery to ensure metadata consistency. The ACD file number for each disk group is 3 (F3).

Continuing Operations Directory (COD)

Cod tracks long-running disk group operations, such as file creation and re-balancing. The range of long-running operations is not suitable for ACD. If a long-running operation fails the Cod entry can cause ASM to revert to the state before the failed operation. For example, ASM can roll back an operation that was not completed to create a file. An RDBMS failure or user behavior can cause this scenario to occur. For disk group rebalancing, if the instance performs a rebalance failure, ASM can restart the rebalance on a node that survives in one cluster, or restart the rebalance after the disk group is mounted in a single instance. The file number of the cod in each disk group is number 4th (F4).

Template Directory

Template directory contains information about all temlate of the disk group. The created disk group supports each of the default file types. If a user adds a template of their own, a new entry will be added. Templatedirectory uses a numeric index number.

Each template entry contains the following information:

N Template Name

N File Redundancy

N File Striping Policy

N System Flag

The file number of Template directory in each disk group is number 5th (F5). The default template name is the same as the file type. The file redundancy policy defaults to the redundancy policy for the disk group. The file stripe is specified by default for the file type. System flag is set to the default (or system) template. The user creates the template without setting the system tag.

Alias Directory

Alias directory contains all of the alias's metadata, system aliases, system directories, user directories, and user aliases. It is also numbered using a numeric index.

Alias directory contains the following structure:

n Alias name (ordirectoryname)

N Alias incarnation number

N File Number

N File incarnation number

N Parent Directory

N System Flag

Alias directory has a file number of number 6th (F6) in each disk group. Aliasincarnation is very similar to the incarnation of a file, providing a unique guarantee for aliases or directories that may have the same aliasnumber. System Flag is an alias and directory created by the systems, but does not set system flag for user-created aliases and directories.

Attributesdirectory

Attributedirectory includes the property metadata for the disk group. This data structure is only available if the disk group Compatible.asm is 11.1 or more than 11.1. For such a disk group, the Attributedirectory file number is 9 (F9). (File numbers 7 and 8 are reserved for future data structures). The Au_size property is actually stored in the disk header because of the boot's original. COMPATIBLE. ASM is stored in PST in 11.1 or later, otherwise it is also stored in the disk header. The Oracledatabase 11g RELEASE 1,compatible.rdbms and Disk_repair_time and their values are stored in the attributedirectory. Additional properties will be supported in future releases.

Staleness Directory

Staleness directory includes metadata for the stalenessregistry mapping table slots for specific disks and clients. The Stalenessdirectory file number is (F12). If necessary, it will be allocated with stalenessregister distribution.

Staleness Registry (SR)

Staleness registry is used to track the offline of the disk causing problems in AU. In the normal-and high-redundancy disk groups and Compatible.rdbms is set to 11.1 or later, registry is a No. 254 file (file 255 is a reserved file). Stalenessregister are created when needed, and can grow dynamically when additional offline disks need to be tuned or new ASM and RDBMS instances are needed.

When the disk is offline, each RDBMS instance gets a slot (slot) about the disk in Stalenessregistry. This slot has a byte corresponding to each AU of the offline disk. The location where the RDBMS is written is exactly where the offline disk is located, and if no matching Bit,rdbms instance has been set, the matching bit will be set for the disk in the Stalenessregistry slot.

When disk online, ASM performs a bitwise OR operation by using the disk online DB instance. Any au have bit settings must be copied from the mirrored extent. Any bit cleaned au is not required as part of the disk online update. Because AU only needs to update the changes when the disk is offline, it is more efficient to replace a disk online with an old one than to add a new disk.

Summarize

The ASM Disk Group is a self-describing entity that holds metadata from all disk groups. Each disk has a small subset of physical metadata. The rest of the metadata-the metadata stored in the virtual address-is stored in an ASM file, which enables the metadata to take advantage of the same metadata distribution and redundancy characteristics through the data files stored in the disk group.

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