Performance and Sizing
31
Calculating Backup Windows
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Volume Calculations--Backup windows can be set at virtually 24 hours per day with the
EBS due to the use of a separate Storage Area Network (SAN) for data movement.
However, many administrators prefer to schedule backups at off hours for management
reasons. To calculate the time needed to perform various backup jobs, the backup rate, as
defined in the Backup Formula section, must be compared to the data sets being backed
up.
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Tape Change Adjustment--Backup windows are determined by the total elapsed time
required to backup sets of data. The number of DLT Drives can be increased by adding
Tape Libraries to the EBS to meet the most demanding needs. A 3% reduction in
performance should be applied to all backups that exceed the volume of one tape.
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Incremental or Differential Adjustment--Incremental and differential backups must
compare archive bits of all files in the 180 GB data set and only back up the files that have
changed since the last differential or full backup. A 14% reduction in performance should
be applied to all Incremental and Differential backups.
IMPORTANT: Real world effects on Incremental and Differential backups will vary depending
on the percentage of changed files in each data set.
More Information
For detailed information and data for Lights Out testing see the whitepaper entitled Sizing the
Compaq StorageWorks Enterprise Backup Solution (Part Number
ECG551/0399
) at:
http://www.compaq.com/support/techpubs/whitepapers/.