VERITAS File System

VERITAS File System (referred to as VxFS) is an extent-based, intent logging file system intended for use in UNIX environments that deal with large volumes of data and that require high file system performance, availability, and manageability. VxFS also provides enhancements that make file systems more viable in database environments.

The VxFS file system included in this product has all the features of the optional HP OnlineJFS file system product available from HP-UX; however, VxFS also includes Quick I/O, Storage Checkpoints, and Storage Rollback. In this document, the terms "VxFS" and "HP OnlineJFS" are synonymous in all contexts except in relation to Quick I/O, Storage Checkpoints, and Storage Rollback.

The following sections provide a brief overview of VxFS concepts and features that are relevant to database administration. For a more detailed description of VxFS and its complete feature set, see the VERITAS File System Administrator's Guide.

VERITAS Quick I/O

Databases can run on either file systems or raw devices. Database administrators often create their databases on file systems because it makes common administrative tasks (such as moving, copying, and backing up) easier. However, running databases on most file systems significantly reduces database performance.

When performance is an issue, database administrators create their databases on raw devices. VxFS with Quick I/O presents regular, preallocated files as raw character devices to the application. Using Quick I/O, you can enjoy the management advantages of databases created on file systems and achieve the same performance as databases created on raw devices. See Using VERITAS Quick I/O for more information.

Quick I/O can be used on Oracle9i and Oracle 10g. However, if you are using Oracle9i or Oracle 10g, we recommend that you use Oracle Disk Manager.

VERITAS Cached Quick I/O

ached Quick I/O allows databases to make more efficient use of large system memory while still maintaining the performance benefits of Quick I/O. Cached Quick I/O provides an efficient, selective buffering mechanism to back asynchronous I/O. Using Cached Quick I/O, you can enjoy all the benefits of Quick I/O and achieve even better performance.

Cached Quick I/O is first enabled for the file system and then enabled on a per file basis. SeeUsing VERITAS Cached Quick I/Ofor more information.

Extent-Based Allocation

The HFS file system supplied with HP-UX uses block-based allocation schemes that provide good random access to files and acceptable latency on small files. For larger files, like database files, this block-based architecture limits throughput. This limitation makes the HFS file system a less than optimal choice for database environments.

The VxFS file system addresses this performance issue by allocating storage in groups of extents rather than a block at a time. An extent is one or more adjacent blocks of data within the file system. An extent is presented as an address-length pair that identifies the starting block address and the length of the extent (in file system or logical blocks). When storage is allocated to a file on a VxFS file system, it is grouped in extents, as opposed to being allocated a block at a time as with the HFS file system.

By allocating disk space to files in extents, disk I/O to and from a file can be done in units of multiple blocks. This type of I/O can occur if storage is allocated in units of consecutive blocks. For sequential I/O, multiple block operations are considerably faster than block-at-a-time operations. Almost all disk drives accept I/O operations of multiple blocks.

The VxFS file system allocates disk space to files in groups of one or more extents. VxFS also allows applications to control some aspects of the extent allocation for a given file. Extent attributes are the extent allocation policies associated with a file.

For information on how to create preallocated database files using extent attributes, see Preallocating Space for Quick I/O Files Using the setext Command.

Fast File System and Database Recovery

VERITAS File System begins recovery procedures within seconds after a system failure by using a tracking feature called intent logging. This feature records pending changes to the file system structure in a circular intent log. The intent log recovery feature is not readily apparent to users or a system administrator except during a system failure. During system failure recovery, the VxFS fsck utility performs an intent log replay, which scans the intent log and nullifies or completes file system operations that were active when the system failed. The file system can then be mounted without completing a full structural check of the entire file system. Replaying the intent log may not completely recover the damaged file system structure if there was a disk hardware failure; hardware problems may require a complete system check using the fsck utility provided with VERITAS File System.

Online System Administration

The VxFS file system provides online system administration utilities to help resolve certain problems that impact database performance. You can defragment and resize a VxFS file system while it remains online and accessible to users.

Defragmentation Utility

Free resources are originally aligned in the most efficient order possible and are allocated to files in a way that is considered by the system to provide optimal performance. When a file system is active for extended periods of time, new files are created, old files are removed, and existing files grow and shrink. Over time, the original ordering of free resources is lost and the file system tends to spread along the disk, leaving unused gaps or fragments between areas that are in use. This process, known as fragmentation, leads to degraded performance because the file system has fewer choices when selecting an extent (a group of contiguous data blocks) to assign to a file. You should analyze the degree of fragmentation before creating new database files.

VxFS provides the online administration utility fsadm to resolve fragmentation problems. The utility can be run on demand and should be scheduled regularly as a cron job.

Resizing Utility

Changes in database size can result in file systems that are too large or too small for the current database. Without special utilities, expanding or shrinking a file system becomes a a matter of stopping applications, offloading the contents of the file system, rebuilding the file system to a new size, and then restoring the data. Data is unavailable to users while these administrative tasks are performed.

The VxFS file system utility fsadm provides a mechanism to resize file systems without unmounting them or interrupting users' productivity. Because the VxFS file system can only be mounted on one device, expanding a file system means that the underlying device must also be expandable while the file system is mounted. Working with VxVM, VxFS provides online expansion capability.

Cross-Platform Data Sharing

VERITAS Cross-Platform Data Sharing allows data to be serially shared among heterogeneous systems where each system has direct access to the physical devices that hold the data. This feature can be used only in conjunction with VERITAS Volume Manager. See the VERITAS Storage Foundation Cross-Platform Data Sharing Administrator's Guide for more information. Shared or parallel access is possible for read-only data.

Cross-Platform Data Sharing provides the fastest way to use Oracle's Transportable Tablespace (TTS) feature for migrating databases to different platforms in Oracle 10g or for moving sets of tablespaces between databases on the same platform in Oracle9i.

Quality of Storage Service (Optional)

The Quality of Storage Service (QoSS) feature is included with the Enterprise Edition.

The QoSS option is built on the multi-volume support technology introduced in this release. Using QoSS, you can map more than one device to a single file system. You can then configure policies that automatically relocate files from one device to another, or relocate files by running file relocation commands. Having multiple devices lets you determine where files are located, which can improve performance for applications that access specific types of files and reduce storage-related costs.

Support for Large File Systems and Large Files (Optional)

Support for large file systems is included with the Enterprise Edition.

In conjunction with VxVM, VxFS can support file systems up to two terabytes in size. For large database configurations, this eliminates the need to use multiple file systems because of the size limitations of the underlying physical devices.

Changes implemented starting with the VxFS Version 3 disk layout have greatly expanded file system scalability, including support for large files.You can create or mount file systems with or without large files by specifying either the largefiles or nolargefiles option in mkfs or mount commands. See Creating a VxFS File System for more information.

Multi-Volume File System Support

The multi-volume file system (MVS) feature allows several volumes to be represented by a single logical object. All I/O to and from an underlying logical volume is directed by way of volume sets. A volume set is a container for multiple different volumes. This feature can be used only in conjunction with VERITAS Volume Manager.

Storage Checkpoint and Storage Rollback

The Storage Checkpoint and Storage Rollback features are included with the Enterprise Edition. With the Standard Edition, they can be purchased as part of the VERITAS FlashSnap option.

VERITAS File System provides a Storage Checkpoint facility that allows you to create a persistent, point-in-time image of all user files in a file system---the Storage Checkpoint remains even after the file system is unmounted or the system is rebooted. Storage Checkpoints present a view of a file system at a point in time, and subsequently identify and maintain copies of the original file system blocks. Instead of using a disk-based mirroring method, Storage Checkpoints save disk space and significantly reduce I/O overhead by using the free space pool available to a file system.

The time required to create a Storage Checkpoint is typically only a couple of seconds. After a Storage Checkpoint is created, a consistent database backup image is made and the database can then resume its normal operation.

The Storage Rollback facility can then be used for rolling back the file system image to the point in time when the Storage Checkpoints were taken. In addition, Storage Checkpoints also keep track of the block change information that enables incremental database backup at the block level.

Storage Checkpoints are writable, and can be created, mounted, and removed. Performance enhancements in maintaining Data Storage Checkpoints (Storage Checkpoints that are complete images of the file system) makes using the Storage Rollback feature easier and more efficient, therefore more viable for backing up large databases.

Multi-Volume File System (MVS) Storage Checkpoint creation allows database backups without having to shut down the database.

MVSs provide the ability to create and administer Storage Checkpoint allocation policies. Storage Checkpoint allocation policies specify a list of volumes and the order in which to allocate Storage Checkpoint data to them. These allocation policies can be used to control where a Storage Checkpoint is created, allowing for separating Storage Checkpoint metadata and data onto different volumes. They can also be used to isolate data allocated to a Storage Checkpoint from the primary file system, which can help prevent the Storage Checkpoint from fragmenting space in the primary file system.

For more information on understanding and using Storage Checkpoints, see Using Storage Checkpoints and Storage Rollback. For more information on using VxDBA and the GUI to manage Storage Checkpoints and Storage Rollback, see Using the VERITAS Storage Foundation for Oracle Graphical User Interface and Using the VxDBA Utility.

Storage Checkpoint File System Restores

Storage Checkpoints can be used by backup and restore applications to restore either individual files or an entire file system. Restoring from Storage Checkpoints can recover data from incorrectly modified files, but typically cannot be used to recover from hardware damage or other file system integrity problems. File restoration can be done using the fsckpt_restore(1M) command. See the VERITAS File System Administrator's Guide for more information.

Quotas

VxFS supports quotas, which allocate per-user and per-group quotas and limit the use of two principal resources: files and data blocks. You can assign quotas for each of these resources. Each quota consists of two limits for each resource:

• The hard limit represents an absolute limit on data blocks or files. A user can never exceed the hard limit under any circumstances.
• The soft limit is lower than the hard limit and can be exceeded for a limited amount of time. This allows users to temporarily exceed limits as long as they fall under those limits before the allotted time expires.

You can use quotas to limit the amount of file system space used by Storage Checkpoints. With VERITAS Storage Foundation for Oracle, you can enable, disable, set, and display quota values for a single file system, for multiple file systems, or for all file systems in a database using the dbed_ckptquota command.

For details on using VxFS quotas, see the VERITAS File System Administrator's Guide.

Cluster Functionality (Optional)

File system clustering is an optional, separately licensed feature of VxFS, where one system is configured as a primary server for the file system, and the other members of a cluster are configured as secondaries. All servers access shared disks for file data operations. If the primary server fails, one of the secondary servers takes over the file system operations. See the VERITAS File System Administrator's Guide for more information.