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Using Snapshot copies in the SAN environment

You can use Snapshot copies in the SAN environment when the data within a Data ONTAP LUN is in a consistent state.

About this task

Data ONTAP cannot ensure that the data within a LUN is in a consistent state. That is, Data ONTAP does not know whether an application is accessing the data inside the LUN. Therefore, before creating a Snapshot copy, you need to quiesce the application or file system using the LUN. This action flushes the host file system buffers to disk. Quiescing ensures that the Snapshot copy is consistent.

One way to accomplish this is to use batch files and scripts on a host that has administrative access to the system.

Steps

  1. Make the data within the LUN consistent with the application by quiescing a database, placing the application in hot backup mode, or taking the application offline.
  2. Use the rsh or ssh command in the script to access the system.
  3. Use the snap command to create the Snapshot copy on the system (this takes only a few seconds, regardless of volume size or use).
  4. Return the application to normal operation.
    Snapshot copy scripts can be scheduled to run at specified intervals. On Windows hosts, you can use the Windows Task Scheduler. On UNIX hosts, you can use cron or other utilities. Also, you can use SnapDrive to save the contents of the host file system buffers to disk and to create Snapshot copies. For more information, see the SnapDrive Installation and Administration Guide.