If you have a SAN (Storage Area Network), you may well have a significant amount of data. Backup Exec can only transfer backup data between servers over the LAN (Local Area Network), so how can you speed up this data transfer, and reduce the amount of traffic sent over the LAN?
Suppose you have a number of servers attached to your SAN, and a separate Backup Exec media server, which is not attached to the SAN. All servers are attached to the LAN. The simple method of backing up this configuration is to install the remote agent on each server. When backups run, the data stored on the SAN is read by the agent on the server, and sent to the Backup Exec server. The downsides to this approach are:
- Without a separate backup network, a lot of data traverses your LAN
- The speed of the backup may be limited by the LAQ
- The servers and their SAN disks are busy for the duration of the backup
There are two options that Backup Exec gives you, which allow you to prevent the data traversing the LAN, speeding up backups and reducing network congestion.
Offhost backup is a feature provided by the Advanced Disk-based Backup Option. In order to use it, you need to have transportable snapshots, which requires Windows Enterprise edition, or Symantec Storage Foundation with the Flashsnap option. You also need to attach your Backup Exec media server to the SAN
When a backup runs, a snapshot of the filesystem to be backed up is initiated. This snapshot is then imported by the Backup Exec media server, which then has direct access to the snapshot. When the backup has finished, the snapshot is unmounted.
Offhost backup has the advantage that the SAN-attached servers are not used for the backup (other than the snapshot phase). The Advanced Disk-Based Backup Option is also quite cheap.
Offhost backup can only be used for backing up filesystems, and Microsoft Exchange if using Backup Exec 12. Other databases must be backed up using the remote agent over the LAN.
Shared Storage Option
The Shared Storage Option allows Backup Exec media servers to coordinate their usage of a shared drive. In our scenario, it would be neccessary to make each SAN-attached server a Backup Exec media server, with the Shared Storage Option on each server. The tape drive (if using tape) would also need to be attached to the SAN.
When a backup runs, the Backup Exec media server attaches to the tape drive, and backs up its data to the drive. When the backup of that server finishes, the tape drive is dismounted, and becomes available for the next Backup Exec media server to use.
This method has the advantage that the requirements for transportable snapshots are not required. However, the number of Backup Exec licenses may present a significant cost.