5 Introduction to Oracle ACFS

About Oracle ACFS

Oracle ACFS is designed as a general-purpose, single-node and clusterwide file system that delivers support for customer file system application data maintained outside of the Oracle Database. Users and applications can access and manage Oracle ACFS using native operating system file system application programming interfaces (APIs) and command-line interface (CLI) tools. Users can also manage Oracle ACFS with the Oracle Enterprise Management and Configuration tools.

Oracle ACFS supports large files with 64-bit file and file system data structure sizes leading to exabyte capable file and file system capacities on 64 bit platforms. Variable extent-based storage allocation, high-performance directories contribute to fast performance, and shared disk configurations that provide direct storage paths to Oracle ACFS file data from each cluster member. File system integrity and fast recovery is achieved with Oracle ACFS metadata checksums and journaling. Oracle ACFS is designed as a multi-node, shared file system model that delivers coherent, cached, direct storage paths to Oracle ACFS file data from each cluster member.

Oracle ACFS files systems are typically configured for clusterwide access. File systems, files, and directories are visible and accessible from all cluster members and can be referenced by users and applications using the same path names from any cluster member. This design enables simplified application deployments across cluster members and facilitates both multiple instance cluster applications and high availability (HA) failover of unmodified single-node applications.

Oracle ACFS presents single system file access semantics across cluster configurations. Applications and users on all cluster members are presented with the same view of shared Oracle ACFS file data at all times supported by the Oracle ACFS clusterwide user and metadata cache coherency mechanism.

About Oracle ACFS and Oracle Database Homes

An Oracle ACFS file system can be used for an Oracle Database home file system. The file system can be configured as any Oracle Database home, including a shared or non-shared Oracle Database home in Oracle RAC cluster configurations.

Oracle Database homes created on Oracle ACFS should be located directly under the ORACLE_BASE/acfsmounts mount point location where ORACLE_BASE is the user-specified database directory of the database owner. The Oracle Database base (ORACLE_BASE for database) directory should not be the Oracle grid infrastructure base (ORACLE_BASE for grid) directory or should not be located under the Oracle grid infrastructure base directory (ORACLE_BASE for grid).

One or more Oracle Database homes on Oracle ACFS can be created under the mount point. Each Oracle Database home should be created using a separate Oracle ACFS file system located under the acfsmounts mount point. For example, ORACLE_BASE/acfsmounts/dbhome1 and ORACLE_BASE/acfsmounts/dbhome2 can be configured as two individual file systems mounted on dbhome1 and dbhome2 mount points created under the ORACLE_BASE/acfsmounts mount point.

After the installation of Grid Infrastructure Software and before the installation of the Oracle Database software with Oracle Universal Installer (OUI), you can create an Oracle ACFS file system to be configured for use as an Oracle Database Home. You can use the Oracle ASM Configuration Assistant (ASMCA) to create the Oracle file system or you can perform the general procedure for creating the file system. See "Creating an Oracle ACFS File System for a Database Home" and "Basic Steps to Manage an Oracle ACFS".

After the Oracle ACFS file system is created, the Oracle ACFS-based database home mount point location can be selected as the Oracle Database Home location by browsing to and then choosing the directory during the OUI Database Software installation.

Oracle ACFS file systems can be also configured for use as application homes and Oracle Database homes. However, Oracle ACFS file systems cannot be used for an Oracle base directory or an Oracle grid infrastructure home that contains the software for Oracle Clusterware, Oracle ASM, Oracle ACFS, and Oracle ADVM components.

About Oracle ASM Dynamic Volume Manager

The Oracle ASM Dynamic Volume Manager (Oracle ADVM) provides volume management services and a standard disk device driver interface to clients. File systems and other disk-based applications issue I/O requests to Oracle ADVM volume devices as they would to other storage devices on a vendor operating system.

For more information about Oracle ADVM, see "Overview of Oracle ASM Dynamic Volume Manager".

About the Oracle ACFS Driver Model

An Oracle ACFS file system is installed as a dynamically loadable vendor operating system (OS) file system driver and tool set that is developed for each supported operating system platform. The driver is implemented as a Virtual File System (VFS) and processes all file and directory operations directed to a specific file system.

About the Oracle ACFS Mount Model and Namespace

Oracle ACFS is designed as a hierarchical file system containing files and subdirectories organized into a tree-structured namespace with files at the leaf nodes. The namespace design is a single-file system naming model for both single-node and cluster configurations. This design enables each cluster member to present shared files to cluster applications using the same path names, simplifying multi-node application and user access, and overall file system administration. The Oracle ACFS mount model also accommodates node local mounts and cluster node subset mounts in cluster configurations to accommodate additional customer requirements.

With a primary focus upon the support of customer application files, Oracle ACFS is not for use as root file system of an operating system or boot storage. Otherwise, an Oracle ACFS file system may be mounted into the native operating system file system namespace using either the mount command line tool or an Oracle Enterprise Management tool.

About the Oracle ACFS Mount Registry

The Oracle ACFS mount registry is an operating system independent, multi-platform mount registration facility supporting both supporting both Oracle Restart and Oracle grid infrastructure cluster configurations. File systems that are to be mounted persistently (across reboots) can be registered with the Oracle ACFS mount registry. In cluster configurations, registered Oracle ACFS file systems are automatically mounted by the mount registry, similar to a clusterwide mount table. However, automatic mounting of registered Oracle ACFS file systems are not supported for Oracle Restart configurations. For more information, see "Oracle ACFS and Oracle Restart".

By default, an Oracle ACFS file system that is inserted into the cluster mount registry is automatically mounted on all cluster members, including cluster members that are added after the registry addition. However, the cluster mount registry also accommodates single-node and multi-node (subset of cluster nodes) file system registrations. The mount registry actions for each cluster member mount only registered file systems that have been designated for mounting on that member.

The Oracle ACFS registry resource actions are designed to automatically mount a file system only one time for each Oracle grid infrastructure initialization to avoid potential conflicts with administrative actions to dismount a given file system.

About Oracle ACFS Snapshots

An Oracle ACFS snapshot is an online, read-only, point in time copy of an Oracle ACFS file system. The snapshot copy is space-efficient and uses Copy-On-Write functionality. Before an Oracle ACFS file extent is modified or deleted, its current value is copied to the snapshot to maintain the point-in-time view of the file system.

Oracle ACFS snapshots are immediately available for use after they are created. They are always online while the file system is mounted. As a result, an Oracle ACFS snapshot can support the online recovery of files inadvertently modified or deleted from a file system. With up to 63 snapshot views supported for each file system, flexible online file recovery solutions spanning multiple views can be employed. An Oracle ACFS snapshot can also be used as the source of a file system backup, as it can be created on demand to deliver a current, consistent, online view of an active file system.

Oracle ACFS snapshot storage is maintained within the file system, eliminating the management of separate storage pools for file systems and snapshots. Oracle ACFS file systems can be dynamically resized to accommodate additional file and snapshot storage requirements.

Oracle ACFS snapshots are administered with the acfsutil snap commands. For information about the acfsutil snap commands, see "acfsutil snap create" and "acfsutil snap delete".

You can also manage Oracle ACFS snapshots with Oracle Enterprise Manager. For information about using Oracle Enterprise Manager, see "Managing Oracle ACFS Snapshots with Oracle Enterprise Manager".

About Oracle ACFS and Backup and Restore

Oracle ACFS executes on operating system platforms as a native file system technology supporting native operating system file system application programming interfaces (APIs). As a result, backup applications that access files using the native operating system file system interfaces are able to access and backup Oracle ACFS file systems and other native operating system file systems. Oracle ACFS snapshots can be dynamically created and used to present a consistent, on-line view of an active file system to a backup application.

Backup applications that use interfaces other than the standard operating system interfaces (read or write) are not supported with Oracle ACFS. For example, Windows backup applications that depend upon the presence of reparse points or the Windows Volume Shadow Copy Service (VSS) are not supported.

About Oracle ACFS Integration with Oracle ASM

Oracle ACFS is always configured with Oracle ASM storage and interfaces with Oracle ASM storage through a traditional device file. This device file is presented by the Oracle ASM Dynamic Volume Manager (Oracle ADVM) and is constructed using a dynamic volume file. The Oracle ADVM volume device file is created automatically following the creation of an Oracle ADVM volume. An Oracle ACFS file system is then bound to the Oracle ADVM device file during the file system creation. After an Oracle ACFS is configured and mounted, the file system inherits the Oracle ASM storage management features associated with an Oracle ADVM volume, including dynamic balanced distribution, mirroring and striping, and dynamic resizing.

The Oracle ACFS driver establishes communication with the Oracle ASM instance to receive Oracle ASM status information including Oracle ASM instance and disk group state transitions.

For information about Oracle ACFS and Oracle ASM operations, see "Oracle ACFS and Dismount or Shutdown Operations".

Oracle ACFS and File Access and Administration Security

Oracle ACFS supports both traditional UNIX-style file access control classes (user, group, other) for Linux and UNIX platforms and the Windows Security Model including file access control lists (ACLs) for Windows platforms. Most Oracle ACFS administrative actions are performed by users with either root or Oracle ASM administration privileges for Linux and UNIX platforms and by users with Windows Administrative privileges on Windows platforms. General Oracle ACFS information for file systems can be accessed by any system user.

In support of Oracle ACFS administration, Oracle recommends that the Oracle ASM administrator role is given to a root privileged user, as many common Oracle ACFS file system management tasks including mount, umount, fsck, driver load, and driver unload are root privileged operations. Other privileged Oracle ACFS file system operations that do not require root privileges can be performed by the Oracle ASM administrator. If the Oracle ASM administrator role is not given to a root privileged user, access to Oracle ACFS file systems can be restricted with the norootsuid and nodev mount options.

For information about Oracle ASM privileges, see "About Privileges for Oracle ASM". For information about administering Oracle ACFS, see Chapter 10, "Administering Oracle ACFS With Oracle Enterprise Manager" and Chapter 13, "Oracle ACFS Command-Line Tools".

Oracle ACFS and Grid Infrastructure Installation

Oracle grid infrastructure includes Oracle Clusterware, Oracle ASM, Oracle ACFS, Oracle ADVM, and driver resources software components, which are installed into the Grid Infrastructure Home using the Oracle Universal Installation (OUI) tool.

For information about Oracle ACFS and Oracle Clusterware resources, see "Clusterware Resources and Oracle ACFS Administration".

Oracle ACFS and Grid Infrastructure Configuration

After a Grid Infrastructure installation, Oracle Clusterware is operational and the Oracle ASM Configuration Assistant (ASMCA) can be used to start the Oracle ASM instance and create Oracle ASM disk groups, Oracle ADVM volumes, and Oracle ACFS file systems. Alternatively, Oracle ASM disk groups and Oracle ADVM volumes can be created using SQL*Plus, ASMCMD command line tools, or Oracle Enterprise Manager. File systems can be created using operating system command-line tools or Oracle Enterprise Manager.

Oracle ACFS file systems are configured with Oracle ADVM based operating system storage devices that are created automatically following the creation of an Oracle ADVM dynamic volume file. After a volume file and its associated volume device file are created, a file system can be created and bound to that operating system storage device. Following creation, an Oracle ACFS file system can be mounted, after which it is accessible to authorized users and applications executing file and file system operations.

For an example of the specific actions required to create a file system, see "Basic Steps to Manage an Oracle ACFS". For information about managing Oracle ACFS file systems with ASMCA, see "Managing Oracle ACFS File Systems With Oracle ASM Configuration Assistant". For information about managing Oracle ACFS file systems with Oracle Enterprise Manager, see "Creating Oracle ACFS Volumes and File Systems".

Clusterware Resources and Oracle ACFS Administration

Oracle Clusterware resources support Oracle ACFS, Oracle Kernel Services Driver (OKS), Oracle ADVM startup, the Oracle ACFS cluster mount registry, and Oracle ACFS single file system startup, shutdown, and steady-state actions.

The following list summarizes Oracle ACFS resource-based management.

• The Oracle ACFS, Oracle Kernel Services (OKS), and Oracle ADVM drivers are dynamically loaded when the Oracle ASM instance is started.

  • Oracle ACFS

    This driver processes all Oracle ACFS file and directory operations.

  • Oracle ADVM

    This driver provides block device services for Oracle ASM volume files that are used by file systems for creating file systems.

  • Oracle Kernel Services Driver (OKS)

    This driver provides portable driver services for memory allocation, synchronization primitives, and distributed locking services to Oracle ACFS and Oracle ADVM.

  The drivers are managed as a single resource set.

  For information, see "Oracle ACFS Drivers Resource Management".

• Oracle ACFS file systems listed in the Oracle ACFS mount registry are automatically mounted during Grid Infrastructure initialization and as new mount registry entries are created.

  The registry resource is used to manage activation of the Oracle ACFS mount registry and to support the mount and dismount actions for Oracle ACFS file systems listed in the Oracle ACFS mount registry.

  For information, see "Oracle ACFS Registry Resource Management".

• Individual file systems are either manually mounted or dismounted using an Oracle ACFS or Oracle Clusterware command-line tool, or automatically mounted or dismounted based on a resource dependency action.

  For example, a file system hosting an Oracle Database home can be named in the dependency list of the associated Oracle Database resource such that issuing a start on the database resource results in mounting the dependent Oracle ACFS hosted database home file system.

  For information, see "Oracle ACFS Individual File System Resource Management".

Oracle ACFS and Dismount or Shutdown Operations

It is important to dismount any active file system configured with an Oracle ADVM volume device file before an Oracle ASM instance is shutdown or a disk group is dismounted. After the file systems are dismounted, all open references to Oracle ASM files are removed and associated disk groups can be dismounted or the instance shut down.

If the Oracle ASM instance or disk group is forcibly shut down or fails while an associated Oracle ACFS is active, the file system is placed into an offline error state. If any file systems are currently mounted on Oracle ADVM volume files, the SHUTDOWN ABORT command should not be used to terminate the Oracle ASM instance without first dismounting those file systems. Otherwise, applications encounter I/O errors and Oracle ACFS user data and metadata being written at the time of the termination may not be flushed to storage before the Oracle ASM storage is fenced. If it is not possible to dismount the file system, then you should issue two sync (1) commands to flush cached file system data and metadata to persistent storage before issuing the SHUTDOWN ABORT operation.

Any subsequent attempt to access an offline file system returns an error. Recovering a file system from that state requires dismounting and remounting the Oracle ACFS file system. Dismounting an active file system, even one that is offline, requires stopping all applications using the file system, including any shell references. For example, a previous change directory (cd) into a file system directory. The Linux fuser or lsof commands or Windows handle command list information about processes and open files.

For information about shutting down an Oracle ASM instance, see "Shutting Down an Oracle ASM Instance". For information about dismounting a disk group, see "Mounting and Dismounting Disk Groups".