Replication

Replication occurs when replication is enabled for a deduplicated NAS share or VTL partition and a replication schedule is configured (or manual replication is performed on a regular basis). For replication to occur, the source system must be configured to point to the target system. Similarly, the target system must be configured to accept data from the source system.

To optimize the replication process, deduplicated data is continuously sent in the background from the source system to the target system. However, a snapshot that preserves the file structure of your data is sent to the target system only when a scheduled or manual replication job occurs. A snapshot contains all of the information that is necessary to recreate a share or partition just as it was at the point in time when the snapshot was created.

Caution: A saved snapshot is necessary to recover your data at a later time. For this reason, it is not enough to simply enable replication for a share or partition. You must also configure a replication schedule (recommended) or perform manual replication on a regular basis to send snapshots of the share or partition to the target system.

If the source system ever becomes unavailable, you can recover the share or partition on the target system using a saved snapshot. After you recover a share or partition, it is recreated on the target system and is available for use. Once the source system becomes available again, you can perform a failback operation to restore the share or partition to its original location.

Like replication, Directory/File or Cartridge Based Replication sends data from a NAS share or VTL partition to another system where it can be accessed. However, Directory/File or Cartridge Based Replication differs in a number of important ways:

• Both replication and Directory/File or Cartridge Based Replication must be enabled for the share or partition.
• A unique Sync ID is used to associate the replicated share or partition on the source system with the share or partition that will receive the replicated data on the target system.

• You do not need to schedule or manually perform share or partition through the remote management console. Instead, replication is triggered when a file is closed or a period of time after it is modified (NAS shares), or when a tape cartridge is unmounted (VTL partitions).

  Additional Information

  • For CIFS/SMB shares, a file is replicated immediately after it is closed. For NFS shares, a file is replicated after it has been idle (not accessed) for several minutes.
  • To optimize the replication process, deduplicated data is continuously sent in the background from the source system to the target system. Any remaining data is sent (along with metadata) at the time a file is closed or a tape cartridge is unmounted.
• After files or cartridges are replicated using Directory/File or Cartridge Based Replication, they are automatically recovered on the target system and are immediately available for use. There is no need to first recover the share or partition to access its data.
• Deletions are automatically propagated from the source system to the target system in order to free up space on the target. In addition, you can manually initiate a synchronization from the source system at any time. Synchronizing ensures that the contents of the source share or partition are exactly the same as the target share or partition.

Caution: Cartridge barcodes for all source systems that are replicating to the same target must be unique.

Note: If you delete a share configured for Directory/File Based Replication on the source DXi , the share is not automatically deleted on the target DXi . If you do not want to retain the share on the target DXi , you can manually delete it.

The DXi4700 can duplicate the data on an LSU (logical storage unit) to another location using the OST optimized duplication (OST replication) feature supported by Veritas NetBackup and Backup Exec. If you are using Veritas NetBackup 7.1 or higher, you can configure an LSU for Automatic Image Replication.

For information about configuring and using OST optimized duplication and Automatic Image Replication, see Replicating OST Data.

The DXi4700 can send replicated data to multiple target systems. First, configure up to two replication targets (see Adding a Replication Target). Then, for each share or partition, select which targets to replicate data to—one, both, or neither (see Enabling Replication For a Share or Partition).

Below are three possible scenarios in which multiple replication targets are configured.

All Shares or Partitions Replicate to Multiple Targets

For enhanced disaster recovery, all share or partition on the DXi4700 are configured to replicate to multiple targets. In this scenario, even if one target system is lost, the other target system still retains a full copy of all data on the source DXi4700.

Some Shares or Partitions Replicate to Multiple Targets

For increased flexibility, each share or partition on the DXi4700 is configured to replicate only to the targets where needed. In this scenario, share or partition fall into three categories:

• Some share or partition replicate to Target 1. (They may also replicate to Target 2.)
• Some share or partition replicate to Target 2. (They may also replicate to Target 1.)
• Some share or partition are not replicated.

To replicate all data on a NAS share or VTL partition from a source system to a target system:

1. On the target system, add the source system to the list of allowed replication sources (see Adding a Replication Source).
2. On the source system, specify the target system that will receive replicated data (see Adding a Replication Target).
3. On the source system, create a new share or partition with deduplication enabled (see Adding a NAS Share or Adding a VTL Partition).
4. Enable replication for the new share or partition (see Enabling Replication For a Share or Partition).

5. Before writing any data to the new share or partition, replicate the new share or partition (see Replicating a Share or Partition).

   Quantum recommends that you always replicate a new share or partition immediately after creating it. This establishes the initial data structure on the target system and greatly increases the speed of the first replication.

6. Choose one of the following methods to regularly replicate the new share or partition:

   • (Recommended) Use the Scheduler page to set up a schedule for performing replication automatically after backups complete (see Scheduling a Share or Partition for Replication).
   • Manually perform replication at frequent intervals (see Replicating a Share or Partition).

After replication, a snapshot is sent to the target system. You can use the snapshot to recover the replicated share or partition on the target system (see Task Overview: Recovering a Replicated Share or Partition) or restore the share or partition to its original location on the source system (see Task Overview: Performing a share or partition Failback).

Note: To limit the amount of network bandwidth used for replication, enable a constant throttle (see Enabling System Throttling), or schedule replication throttling (see Scheduling Replication Throttling).

To automatically replicate files or cartridges from a source system and immediately recover them for use on a target system:

1. Perform the following steps on the target system:

   1. Add the source system to the list of allowed replication sources (see Adding a Replication Source).
   2. Create a new share or partition with deduplication enabled (see Adding a NAS Share or Adding a VTL Partition).
   3. Enable Directory/File or Cartridge Based Replication for the new share or partition and specify the Sync ID (see or Configuring Directory/File or Cartridge Based Replication).

2. Perform the following steps on the source system:

   1. Specify the target system that will receive replicated data (see Adding a Replication Target).
   2. Create a new share or partition with deduplication enabled (see Adding a NAS Share or Adding a VTL Partition).
   3. Enable Directory/File or Cartridge Based Replication for the new share or partition and specify the Sync ID (see Configuring Directory/File or Cartridge Based Replication).

A file is automatically replicated when it is closed or a period of time after it is modified. A cartridge is automatically replicated after it is unmounted. After replication, the replicated files or cartridges are immediately available on the target system. There is no need to recover the share or partition to make the files or cartridges available.

Caution: Cartridge barcodes for all source systems that are replicating to the same target must be unique.

Note: To limit the amount of network bandwidth used for replication, enable a constant throttle (see Enabling System Throttling), or schedule replication throttling (see Scheduling Replication Throttling).

If a NAS share or VTL partition is lost or damaged on the source system, you can recover it on the target system using a received snapshot. When you recover a share or partition, it is recreated on the target system just as it was at the point in time when the snapshot was saved.

To recover a replicated share or partition:

1. On the target system, select a received snapshot and perform a recover operation (see Recovering a Share or Recovering a Partition).

   The share or partition is now available on the target system.

2. (Optional) Map your backup application to the recovered share or partition on the target system to continue making backups.

3. When the source system is operating correctly again, choose one of the following actions:

   • Failback the share or partition to restore it on the original source system (see Task Overview: Performing a share or partition Failback). Then, if necessary, map your backup application to the restored share or partition on the original source system.
   • Continue to make backups to the recovered share or partition on the original target system. In addition, set up replication to replicate the share or partition back to the original source system (see Task Overview: Setting Up and Performing Replication). In this scenario, the original source system is now the target, and the original target system is now the source.

If a NAS share or VTL partition is lost or damaged on the source system, you can failback the share or partition to the source system using a received snapshot on the target system. When you failback a share or partition, it is restored on the source system just as it was at the point in time when the snapshot was saved.

To perform a share or partition failback:

1. On the original source system, add the original target system to the list of allowed replication sources (see Adding a Replication Source).

   Note: For the purposes of failback, the original source system is now acting as a target because it will receive the snapshot from the original target system.

2. On the original target system, select a received snapshot and perform a failback operation pointing to the original source system, and then recover the share or partition on the original source system (see Performing a Failback For a Share or Performing a Failback For a Partition).

   The share or partition is now available on the original source system.

3. (Optional) If necessary, map your backup application to the restored share or partition on the original source system.