Author: mac

The disk Used Space Directory (USD) – ASM file number 8 – maintains the number of allocation units (AU) used per zone, per disk in a disk group. The USD is split into a set of Used Space Entries (USE). Each USE will maintain a counter for the number of used AUs per disk, per…

The Template Directory – ASM file number 5 – contains information about all file templates for the disk group. There are two types of templates – system and user created. The default (system) templates are always available for each file type supported by ASM. User created templates can be added for a custom template specifications. Each…

The alias directory – ASM file number 6 – provides a hierarchical  naming system for all the files in a disk group. A system file name is created for every file and it is based on the file type, database instance and type-specific information such as tablespace name. User alias may also be created if a…

When the ASM instance needs to make an atomic change to multiple metadata blocks, a log record is written into the ASM active change directory (ACD), which is the ASM metadata file number 3. These log records are written in a single I/O.   The ACD is divided into chunks or threads, and each running…

Some long-running ASM operations, like the rebalance, drop disk, create/delete/resize file, cannot be described by a single record in the ASM active change directory. Those operations are tracked via the ASM continuing operations directory (COD) – the ASM file number 4. There is one COD per disk group.   If the process performing the long-running operation…

The ASM file number 1 – the ASM File Directory – keeps track of all files in a disk group. As the disk groups are independent storage units, each disk group will have its own ASM file directory.   While this is an internal (ASM metadata) file, it is managed like any other file in…

The ASM file number 2 – the ASM disk directory – keeps track of all disks in the disk group. As disk groups are independent storage units, each disk group will have its own ASM disk directory.   As far as the ASM is concerned, the disk directory is just another file. It has its…

ASM ensures that file extents are evenly distributed across all disks in a disk group. This is true for the initial file creation and for file resize operations. That means we should always have abalanced space distribution across all disks in a disk group. Rebalance operation Disk group rebalance is triggered automatically on ADD, DROP and RESIZE disk operations and…

Some ASM commands have the “force” option that allows the administrator to override a default behaviour. While some uses of the force option are perfectly safe and indeed required, some may render your disk group unusable. Let’s have a closer look. Mount force The force option becomes a must when a disk group mount reports missing disks.…

The ASM Metadata Dump Utility – better knows as amdu– is used by Oracle Support and Oracle Development to diagnose and sometimes resolve ASM issues. It can be used to print ASM metadata and extract both ASM metadata and database datafiles from ASM disk groups. The amdu does not depend on the mount state of an ASM instance or the mount state…