O R A C L E F A Q

Frequently Asked Questions Storing Database Files in ACFS on Oracle Database Appliance

Introduction

Oracle ASM Cluster File System (ACFS) provides

unprecedented simplicity, automation and functionality

in storage and file management for all file types

including Oracle database and general-purpose files.

This FAQ provides more information about storing

database files in ACFS on Oracle Database Appliance.

Oracle ACFS was chosen as the primary file system for

Oracle Database Appliance because it provides:

• Increased functionality without requiring additional management

• Equivalent performance to Oracle ASM

• Industry standard and simple user interface

• Database snapshots to quickly and easily provision test and development environments at a fraction of the disk storage required with full database copies

• Advanced functionality for general purpose files such as replication, tagging, encryption, security, and auditing

Performance Oracle ACFS is designed to deliver best possible performance with Oracle databases and general purpose files. Oracle ACFS obtains an extent map list and disk list information from the Oracle ASM instance whenever it opens an ASM file. This means, neither Oracle ASM nor Oracle ACFS are in the I/O path when accessing files on disk. Oracle ACFS caches ASM disk mapping information and uses the mapping on subsequent ACFS I/O operations to directly read and write to ASM disk group disks.

Comprehensive internal benchmarks using OLTP and DSS workloads have proven the performance of Oracle ACFS and ASM to be similar. The charts below reflect ACFS vs. ASM performance for some OLTP workloads. Refer to the “Benefits of Oracle ACFS” white paper for more details on how ACFS performs relative to ASM.

The following chart shows performance based on OLTP workload. As you can see, the throughput performance and transaction response time are almost identical regardless of whether the database use ACFS or ASM directly.

In a virtualized Oracle Database Appliance, the storage is directly attached to the VM hosting the databases (ODA_Base). This provides I/O performance on par with a bare metal deployment of Oracle Database Appliance for

O R A C L E F A Q

2 STORING DATABASE FILES IN ACFS ON ORACLE DATABASE APPLIANCE

databases in ODA_Base. The shared repository is created in ODA_Base using ACFS, but is then exported to Dom0 and then made available as virtual storage to individual VMs. It is the additional overhead of these exports that impacts performance, not ACFS. This overhead is acceptable for hosting VM Images and templates, as these operations do not require high I/O performance. However, you should not attempt running an I/O intensive workload (for example, a database) against virtual storage based on the shared repository. All databases should reside in ODA_Base.

Question and Answer Q: Why did Oracle switch from ASM to ACFS for storing

database data files on Oracle Database Appliance?

A: ACFS is built on top of ASM, and provides all the benefits of ASM plus the benefits of ACFS. These include space-efficient snapshots of database files for test and development. The latest releases of ACFS support direct I/O, so there is no performance penalty. In other words, ACFS provides all the benefits and more, without any cost.

Q: Why not give customers a choice of ASM or ACFS for database files?

A: Oracle Database Appliance is an appliance, which means we’ve put together a configuration that works best for most customers, without tuning and tweaking. We test that configuration extensively, to ensure users get the best and most reliable experience. That requires choosing a single configuration, so we can focus our development and testing resources on that configuration. Offering a choice of storage dilutes those development and testing efforts, leading to a less functional and less reliable product for all.

Q: In the past, Oracle said ASM was better for database files than a file system. Why now use a file system?

A: ASM was introduced with Oracle 10g to solve the storage management problem for database files. It added features that ensured there would be no I/O bottlenecks, that storage was highly available and resilient, and could be expanded or migrated without downtime. Existing file systems could not provide these benefits. However, in Oracle 11g Release 2, Oracle introduced the ASM Cluster File System (ACFS), built on top of ASM. It inherits all the benefits of ASM, and adds additional features and functionality. With the recent addition of Direct I/O, it provides features and performance comparable to ASM.

Q: Doesn’t ACFS add additional management burden by introducing a file system that requires maintenance?

A: No. Appliance Manager (OAK) automatically manages the file systems. When the first non-CDB database of version 11.2.0.4.2 or greater is created, three default file systems are created automatically in the Oracle Database Appliance ASM disk groups (DATA, RECO, and REDO). The associated database files for each non-CDB database are created in these three ACFS file systems instead of in the ASM disk groups directly. For each CDB database that is created, three additional file systems in DATA, REDO, RECO are created for the database files.

Q: Does the DBA now have to manage database files stored in ACFS?

A: ACFS in the Oracle Database Appliance requires no administration. The Appliance Manager automatically manages the storage; including ACFS file systems and the underlying ASM diskgroups.

Q: Why are existing databases not moved to ACFS automatically after an upgrade to Appliance Manager12.1.2?

A: Existing databases after an upgrade to Appliance Manager 12.1.2 are left in ASM because it would take additional downtime to migrate them to ACFS. Customers may choose to migrate them to ACFS at a later time.

Q: How do I migrate a database from ASM or from another server to ACFS on ODA?

A: You must first create the proper directories to receive the database files before you can migrate them to ACFS on Oracle Database Appliance. This will be automated in the next release of the Database Appliance, but in the mean time, the steps are documented in the white paper “Steps to Migrate Non-CDB Databases to ACFS on Oracle Database Appliance 12.1.2.”

Q: Can I leave my existing databases in ASM while creating new database in ACFS?

A: Yes, both types of databases can coexist on the same appliance. There is no need to move an existing database to ACFS. However, if a database remains in ASM, you cannot clone it using snapshot functionality.

O R A C L E F A Q

Oracle Corporation, World Headquarters Worldwide Inquiries 500 Oracle Parkway Phone: +1.650.506.7000 Redwood Shores, CA 94065, USA Fax: +1.650.506.7200

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