21.2. Selecting and Installing Hardware

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The main factor driving backup hardware selection is the relationship of performance to cost. Speed is an essential component of performance, because the faster the drive system, the faster the backup. Backup performance can be almost tripled (from 30 to 84.5GB/hr) with hardware that provides data to the tape drives quickly. Performance also can be increased with multiple jobs, but only with adequate feed speed.

Unattended backups can significantly reduce administrative costs. Deploying sufficient backup capacity and automation, if needed, to make unattended backups possible is often a significant cost saver for the long term.

For unattended backups, the tape drive and media must meet backup requirements in terms of overall storage capacity and backup performance. Both performance and capacity vary with the type of drive technology selected.

When deciding the hardware most suited to your backup solution, consider also whether backups will be made of individual user data. Because large hard drives can hold gigabytes of software, backing up a user's hard drive could be a time-consuming task, even if it is automated. Related to this is the extra network bandwidth consumed by pulling such large amounts of data over the company network. If project files are being centrally stored on a server, the ideal solution is to back up that data and leave client backups up to the individual user.

Although an autoloader option will increase the cost of the digital audiotape (DAT) backup, it will make unattended backups much easier. Depending on the size of the magazine, tapes could be loaded in the order desired to make a week's worth of backups completely automated.

21.2.1 Calculating Required Performance

Performance requirements determine the type of tape drive you should use. You can calculate your performance needs by dividing the amount of information (in gigabytes) that must be backed up by the size of the backup window (in hours), as shown in Figure 21-1. This simple calculation yields the required performance as an overall transfer rate expressed in GB/hr.

Figure 21-1. Required transfer rate formula.


Consider these factors when choosing the type of tape drive you will use:

  • The maximum capacity of uncompressed data that each drive can store on a cassette

  • The transfer rates for reading and writing uncompressed data with each drive

  • Typical system transfer rates when performing a local backup using each drive in a system

  • The typical time for that system to perform a 10GB backup using each of the drives

  • The number of tape cartridges that must be loaded and unloaded during the backup operation

By comparing the results of the required transfer rate with typical backup performance rates of the drive, you can determine whether the backup performance you need is achievable.

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    HP ProLiant Servers AIS. Official Study Guide and Desk Reference
    HP ProLiant Servers AIS: Official Study Guide and Desk Reference
    ISBN: 0131467174
    EAN: 2147483647
    Year: 2004
    Pages: 278

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