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Disk Space and Backup Software
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This chapter:
• Gives general guidelines for predicting how much disk space your site may use over time.
• Explains how to deal with restorer components that run out of disk space.
• Describes Data Domain Space Usage graphs.
Note Data Domain offers guidance on setting up third-party backup software and backup servers
for use with a restorer. Because such information tends to change often, it is available on the
Data Domain Support web site (http://support.datadomain.com/). See the Technical Notes
section on the web site.
Space Management
A restorer is designed as a very reliable online cache for backups. As new backups are added to the
system, old backups are removed. Such removals are normally done under the control of backup
software (on the backup server) based on the configured retention period. The process with a
restorer is very similar to tape policies where older backups are retired and the tapes are reused for
new backups.
When backup software removes an old backup from a restorer, the space on the restorer becomes
available only after the restorer internal weekly clean function reclaims disk space. A good way to
manage space on a restorer is to retain as many online backups as possible with some headroom
(about 20% of total space available) to allow for data growth over time.
Data growth on a restorer is primarily affected by:
• The size and compressibility of the primary storage that you are backing up.
• The retention period that you specify with the backup software.
If you backup volumes totaling over 4 TB in size or the retention time for volumes that do not
compress well is greater than four months, backups may fill space on a restorer more quickly than
expected.
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