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Chapter 3: Backup and RecoveryPerformanceOur backup options assume that the backup device is local to the database server. A backupperformed over a network will be affected by network topology, overhead, and traffic.Rarely is the full capacity of the network available. If a backup is done over the network, itwill decrease performance for other network users. Although technically possible,performing a backup over a network is beyond the scope of this guidebook.All of the backup options attempt to eliminate the bottleneck at the backup device. Thebackup device, usually a tape drive, is the throughput-limiting device.The table below contains capacity and throughput values to help you plan tape driveselection:TypeCapacity (GB)(native/compressed)Rate (GB/hr)(native/compressed)DAT (DDS-2) 4 / 6.8 1.8 / 3.1DAT (DDS-3) 12 / 20.4 3.6 / 6.1DLT 4000 20 / 34 5.4 / 9.2DLT 7000 35 / 60 18 / 30.6DLT 8000 40/68 21.6/36.7The compressed capacity values in this table assume the use of hardware compression anduse a more conservative 1.7x ratio, as opposed to the typical 2x compression ratio. Theactual compression ratio and rate depends on the nature of the file and how much it can becompressed.A 20 GB database with only 9 GB of data will only require 9 GB of tape space. As thevolume of data in the database increases, so will the tape space requirement. However, ifyou are backing up at the operating system level, the entire file is being backed up.Therefore, you will need to provide tape space for the entire 20 GB database.As technology advances, and the capacity and throughput of tape drives increases, thesevalues will become obsolete. We recommend that you investigate what is currently availableat the time of your purchase.Advantages:Faster and larger capacity tape drives allow you to back up an entire database on a singletape cartridge in a reasonable period of time (for example, a two-hour backup of a 60 GBdatabase to a DLT7000).System Administration Made Easy3–21