Author: mac

Oracle Database version 12c has been released, which means a brand new version of ASM is out! Notable new features are Flex ASM, proactive data validation and better handling of disk management operations. Let’s have an overview with more details in separate posts. Flex ASM No need to run ASM instances on all nodes in…

Starting with version 12.1, ASM replicates the physically addressed metadata. This means that ASM maintains two copies of the disk header, the Free Space Table and the Allocation Table data. Note that this metadata is not mirrored, but replicated. ASM mirroring refers to copies of the same data on different disks. The copies of the physical metadata are on the same disk,…

The ASM Free Space Table (FST) provides a summary of which allocation table blocks have free space. It contains an array of bit patterns indexed by allocation table block number. The table is used to speed up the allocation of new allocation units by avoiding reading blocks that are full. The FST is technically part…

Every ASM disk contains at least one Allocation Table (AT) that describes the contents of the disk. The AT has one entry for every allocation unit (AU) on the disk. If an AU is allocated, the Allocation Table will have the extent number and the file number the AU belongs to. Finding the Allocation Table…

The Partnership and Status Table (PST) contains the information about all ASM disks in a disk group – disk number, disk status, partner disk number, heartbeat info and the failgroup info (11g and later). Allocation unit number 1 on every ASM disk is reserved for the PST, but only some disks will have the PST data. PST…

An ASM instance manages the metadata needed to make ASM files available to Oracle databases and other ASM clients. ASM metadata is stored in disk groups and organised in metadata structures. These metadata structures consist of one or more ASM metadata blocks. For example, the ASM disk header consist of a single ASM metadata block.…

When diagnosing ASM issues, it helps to know a bit about the setup – disk group names and types, the state of disks, ASM instance initialisation parameters and if any rebalance operations are in progress. In those cases I usually ask for an HTML report, that gets produced by running the SQL script against one…

Password file authentication for Oracle Database or ASM can work for both local and remote connections. In Oracle version 12c, the password files can reside in an ASM disk group. The ASM metadata structure for managing the passwords is the ASM Password Directory – ASM metadata file number 13. Note that the password files are…

Starting with Oracle Database version 11.2, an ASM disk group can be used for hosting one or more cluster file systems. These are known as Oracle ASM Cluster File Systems or Oracle ACFS. This functionality is achieved by creating special volume files inside the ASM disk group, which are then exposed to the OS as…

Starting with ASM version 11.2, the ASM spfile can be stored in an ASM disk group. Indeed, during a new ASM installation, the Oracle Universal Installer (OUI) will place the ASM spfile in the disk group that gets created during the installation. This is true for both Oracle Restart (single instance environments) and Cluster installations.…