SnapManager overview

What SnapManager does

SnapManager is the data management tool that integrates Network Appliance SnapDrive 2.0 and 2.0.1 technology to provide a data management solution for Lotus Domino databases. It dramatically boosts the availability, scalability, and reliability of Domino servers. SnapManager provides near-instantaneous hot backup and rapid restoration of Domino servers by building on the online Snapshot^TM technology from Network Appliance.

The following figure illustrates the relationship between Network Appliance filers, SnapDrive 2.0 and 2.0.1, and SnapManager for Lotus Domino.

Note
The SnapDrive 2.0 reference in the illustration includes SnapDrive 2.0.1 as well.

How SnapManager and SnapDrive work together

The SnapDrive software integrates with the Microsoft® NTFS Volume Manager to enable use of filers as virtual disks for data storage in the Windows 2000 environment. SnapDrive provides the underlying layer of support for SnapManager. As such, it is transparent to the SnapManager application.

When to use SnapManager

When both SnapDrive and SnapManager are installed on your server, you must use SnapManager for all snapshots and related operations. For example, you use SnapManager to establish your Domino Data directory on virtual disks on a filer and to back up and restore virtual disks on the filer. In this case, SnapDrive is used to create, connect, and expand the virtual disk that hosts the Domino server.

If you do not use SnapManager to migrate your Domino Data directory and transaction logs to virtual disks and then back them up, the correct information required by SnapManager is not available to restore the Data directory.

When to use SnapDrive

SnapDrive manages virtual disks on a filer, making these disks available as ordinary local disks on the Windows 2000 host server. This allows the server to interact with the virtual disks as if they were directly attached, physical disks. You can use SnapDrive to create and manage virtual disks--to create and change the size of virtual disks and to connect and disconnect virtual disks. For information about how to perform these tasks using SnapDrive, see the SnapDrive Installation and Administration Guide appropriate for your version of SnapDrive.

SnapManager modules

SnapManager consists of the following modules:

Domino server add-in

The server add-in module is deployed on the same physical machine as the Domino server. The server module uses the Domino server API for add-ins. The server module is responsible for managing all backup and restore activity.

Client interface

The client interface is the user interface portion of SnapManager for Lotus Domino. The client interface enables you to manage and schedule snapshots and restores against a properly configured Domino server. The client interface communicates with the server on a Windows 2000 socket, which uses a TCP/IP protocol. This enables you to manage and schedule snapshots and restores from any machine that has a network connection to the server.

How SnapManager works with other backup methods

Because backups reside on disk instead of tape, SnapManager technology should be employed as a complement to conventional backup processes.

SnapManager backups are not intended to replace periodic disaster recovery measures. NDMP or Dump are the most efficient methods for creating archives of the virtual disk drive files.

How SnapManager works with snapshots used as backups

A snapshot is a point-in-time, read-only copy of a Domino Data directory stored on a filer volume. SnapManager Backup uses snapshot functionality to create real-time, online, read-only copies of the Domino Data directory. Snapshots enable you to restore your Domino Data directory rapidly if you encounter data corruption or other problems.

The following figure provides an example of how snapshots work.

Example

Suppose you take a snapshot of a file named file.txt that spans four disk blocks in the active file system. Initially, the snapshot version of file.txt and the version in the active file system are identical: the same blocks on disk store both versions, so the snapshot version of file.txt consumes no additional disk space.

Now suppose that you make a modification to file.txt that affects only one of the four disk blocks. The new data cannot overwrite the original block because that block is needed as part of the snapshot. So the new data is written to a new disk block and the file's inodes are updated accordingly. The active file system inodes now reference the three original disk blocks that have not been touched since the snapshot, plus the one new block. The snapshot inodes still reference the original four blocks.

If you delete file.txt, the blocks holding its data are no longer part of the active file system, but they are still part of the snapshot; deleting file.txt from the active file system does not free any disk space until the snapshot is deleted.

How SnapManager safeguards data

Under SnapManager, the Domino Data directory and transaction logs reside on a virtual disk created on the filer and formatted with the New Technology File System (NTFS). The virtual disk can be either a Virtualized Local Disk (VLD), or a Logical Unit Number (LUN), which uses Fibre Channel Protocol (FCP). A VLD is used to store data on a filer in an Ethernet environment. A LUN is a storage target device in a Fibre Channel environment.

To the filer, a virtual disk is one big file. Filers use battery-protected nonvolatile RAM (NVRAM) to protect incoming file system I/O operations. The contents of NVRAM are flushed to disk at regular intervals--more frequently if the NVRAM fills up, even during periods of inactivity. This ensures that the file system is always in a consistent state. The filer's WAFL® file system guarantees that the contents of NVRAM are always written to disk, even during a power failure.