VERITAS Software Used in Point-In-Time Copy Scenarios

This guide provides a number of example scenarios that illustrate how to implement point-in-time copy solutions. The following table shows the VERITAS products that may be used with a VERITAS FlashSnap license to provide the required functionality in different environments:

VERITAS Storage Foundation for databases is required if you want to use the VERITAS Quick I/O, VERITAS Extension for Oracle Disk Manager (ODM), VERITAS QuickLog^TM, Storage Checkpoints and management interface features to enhance database performance and manageability.

The VERITAS Clustering Functionality for VxVM and VERITAS Cluster File System features of VERITAS Storage Foundation for Cluster File System and Cluster File System HA allow you to share data within a cluster. The HA version uses VERITAS Cluster Server to allow you to configure automated application and storage failover to provide continuous availability of service.

The following non-cluster specific components are used in the sample scenarios:

• VERITAS Volume Manager (VxVM) is a disk management subsystem that supports disk striping, disk mirroring, and simplified disk management for improved data availability and superior performance. The FlashSnap license enables the use of the Persistent FastResync and Disk Group Split/Join features of VxVM.
• VERITAS File System (VxFS) is a high-performance, fast-recovery file system that is optimized for business-critical database applications and data-intensive workloads. VxFS offers online administration, letting you perform most frequently scheduled maintenance tasks (including online backup, resizing, and file system changes) without interrupting data or system availability. The FlashSnap license enables the use of the Storage Checkpoints feature of VxFS.

You can also use the following cluster-specific components with the sample scenarios where required:

• VERITAS Cluster Server (VCS) is a high-availability (HA) solution for cluster configurations. VCS monitors systems and application services, and restarts services on a different cluster node (failover) in the event of either hardware or software failure. It also allows you to perform general administration tasks such as making nodes join or leave a cluster.

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  Note    On HP-UX, MC/ServiceGuard may be configured as the cluster monitor.

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• VERITAS Clustering Functionality for VxVM (CVM) allows multiple hosts to simultaneously access and manage a given set of disks that are under the control of VERITAS Volume Manager.
• VERITAS Cluster File System (CFS) allows cluster nodes to share access to the same VxFS file system. CFS is especially useful for sharing read-intensive data between cluster nodes.

If you require a backup solution, the following VERITAS software is recommended:

• VERITAS NetBackup^TM DataCenter provides mainframe-class data protection for corporate data centers. NetBackup DataCenter allows you to manage all aspects of backup and recovery, and allows consistent backup policies to be enforced across your organization. Optional NetBackup ServerFree Agents enhance NetBackup DataCenter to provide data protection for frozen image data such as VxVM snapshot mirrors. They can also be used to offload backup processing to NetBackup media servers or third-party copy devices over Fibre Channel networks.
• VERITAS NetBackup BusinesServer provides protection for small to medium-size server installations. It does not provide integrated support for backing up VxVM snapshot mirrors or for offloading backup processing. However, you can use it to back up snapshot volumes that have been created from snapshot mirrors.

For more information about installing and configuring these products see the following documentation:

• VERITAS Storage Foundation for Cluster File System Installation and Configuration Guide
• VERITAS Storage Foundation for DB2 Database Administrator's Guide
• VERITAS Storage Foundation for DB2 Installation Guide
• VERITAS Storage Foundation for Oracle Database Administrator's Guide
• VERITAS Storage Foundation for Oracle Installation Guide
• VERITAS Storage Foundation for Sybase Database Administrator's Guide
• VERITAS Storage Foundation for Sybase Installation Guide
• VERITAS Storage Foundation Installation Guide
• VERITAS File System Administrator's Guide
• VERITAS NetBackup DataCenter Installation Guide
• VERITAS NetBackup DataCenter System Administrator's Guide
• VERITAS NetBackup ServerFree Agent System Administrator's Guide
• VERITAS NetBackup for Oracle ServerFree Agent System Administrator's Guide
• VERITAS NetBackup BusinesServer Getting Started Guide
• VERITAS NetBackup BusinesServer System Administrator's Guide
• VERITAS Volume Manager Administrator's Guide

Persistent FastResync of Volume Snapshots

VERITAS Volume Manager allows you to take multiple snapshots of your data at the level of a volume. A snapshot volume contains a stable copy of a volume's data at a given moment in time that you can use for online backup or decision support. If Persistent FastResync is enabled on a volume, VxVM uses a FastResync map to keep track of which blocks are updated in the volume and in the snapshot. If the data in one mirror is not updated for some reason, it becomes out-of-date, or stale, with respect to the other mirrors in the volume. The presence of the FastResync map means that only those updates that the mirror has missed need be reapplied to resynchronize it with the volume. A full, and thereby much slower, resynchronization of the mirror from the volume is unnecessary.

When snapshot volumes are reattached to their original volumes, Persistent FastResync allows the snapshot data to be quickly refreshed and re-used. Persistent FastResync uses disk storage to ensure that FastResync maps survive both system and cluster crashes. If Persistent FastResync is enabled on a volume in a private disk group, incremental resynchronization can take place even if the host is rebooted.

Persistent FastResync can track the association between volumes and their snapshot volumes after they are moved into different disk groups. After the disk groups are rejoined, Persistent FastResync allows the snapshot plexes to be quickly resynchronized.

For more information, see the VERITAS Volume Manager Administrator's Guide.

Instant Volume Snapshots

The traditional type of volume snapshot that was provided in VxVM is of the third-mirror type. This name comes from its original implementation by adding an additional plex to a mirrored volume. After the contents of the third-mirror (or snapshot plex) had been synchronized from the original plexes of the volume, it could be detached as a snapshot volume for use in backup or decision support applications. Enhancements to the snapshot model allowed snapshot volumes to contain more than a single plex, reattachment of a subset of a snapshot volume's plexes, and persistence of FastResync across system reboots or cluster restarts.

Release 4.0 of VxVM introduced instant snapshots, which offer advantages over traditional third-mirror snapshots. The benefits of instant snapshots include immediate availability for use, quick refreshment, and easier configuration and administration. Full-sized instant snapshots are similar to third-mirror snapshots in that they are the same length as the original volume.

Space-optimized instant snapshots require less space than full-sized snapshots by recording changed regions in the original volume to a storage cache. As the original volume is written to, VxVM preserves its data in the cache before the write is committed.

For more information, see the VERITAS Volume Manager Administrator's Guide.

Disk Group Split/Join

One or more volumes, such as snapshot volumes, can be split off into a separate disk group and deported. They are then ready for importing on another host that is dedicated to off-host processing. This host need not be a member of a cluster but it must have access to the disks on which the volumes are configured. At a later stage, the disk group can be deported, re-imported, and joined with the original disk group, or with a different disk group.

For more information, see the VERITAS Volume Manager Administrator's Guide.

Storage Checkpoints

A Storage Checkpoint is a persistent image of a file system at a given instance in time. Storage Checkpoints use a copy-on-write technique to reduce I/O overhead by identifying and maintaining only those file system blocks that have changed since a previous Storage Checkpoint was taken. Storage Checkpoints have the following important features:

• Storage Checkpoints persist across system reboots and crashes.
• A Storage Checkpoint can preserve not only file system metadata and the directory hierarchy of the file system, but also user data as it existed when the Storage Checkpoint was taken.
• After creating a Storage Checkpoint of a mounted file system, you can continue to create, remove, and update files on the file system without affecting the image of the Storage Checkpoint.
• Unlike file system snapshots, Storage Checkpoints are writable.
• To minimize disk space usage, Storage Checkpoints use free space in the file system.

Storage Checkpoints and the Storage Rollback feature of VERITAS Storage Foundation for Databases enable rapid recovery of databases from logical errors such as database corruption, missing files and dropped table spaces. You can mount successive Storage Checkpoints of a database to locate the error, and then roll back the database to a Storage Checkpoint before the problem occurred. For more information, see Database Recovery and the VERITAS Storage Foundation Administrator's Guide.

VERITAS NetBackup for Oracle Advanced BLI Agent uses Storage Checkpoints to enhance the speed of backing up Oracle databases. For more information, see the VERITAS NetBackup for Oracle Advanced BLI Agent System Administrator's Guide.

For more information about the implementation of Storage Checkpoints, see the VERITAS File System Administrator's Guide.

VERITAS FlashSnap Agent for Symmetrix

The EMC TimeFinder product from EMC is a business continuance solution that allows you to create and use copies of EMC Symmetrix devices while the standard devices remain online and accessible. Business Continuance Volume (BCV) devices contain copies of Symmetrix standard (STD) devices and provide redundancy. You can temporarily detach the BCV mirrors and use the BCVs to perform backups, testing, and other administrative tasks.

VERITAS FlashSnap Agent for Symmetrix provides a set of commands that allow you to use the EMC TimeFinder split and restore operations in conjunction with VxFS file systems and VxVM disk groups and volumes that have been created on Symmetrix STD devices.

You can use the commands in VERITAS FlashSnap Agent for Symmetrix to:

• Associate a disk group with a BCV disk group, or Symmetrix STD devices in a disk group with identical BCV devices.
• Initiate TimeFinder mirroring for Symmetrix STD devices in a disk group.
• Split Symmetrix STD devices from their BCV devices and create duplicate volumes on the BCV devices. You can use the resulting BCV volumes for administrative tasks such as backups and testing.
• Reattach and resynchronize the STD and BCV devices. The devices can be remirrored from the STD copy or restored from the BCV copy.
• Detach the STD devices from their BCV devices.

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  Note    The VERITAS FlashSnap Agent for Symmetrix software is available with the VERITAS Storage Foundation for Oracle product. It is not currently available for DB2 or Sybase databases.

A valid SYMCLI license key must be obtained from EMC to use EMC TimeFinder.

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The VERITAS Cluster Server Agents for VERITAS FlashSnap Agent for Symmetrix are add-ons to VERITAS Cluster Server that enable automatic recovery of FlashSnap Agent for Symmetrix operations.

For more information, see the following documents that are installed with the VRTSfasdc package:

• VERITAS FlashSnap Agent for Symmetrix Installation Guide
• VERITAS FlashSnap Agent for Symmetrix Administrator's Guide
• VERITAS Cluster Server Agents for VERITAS FlashSnap Agent for Symmetrix Installation and Configuration Guide