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34 Adding TL895 Libraries to the Compaq Enterprise Backup Storage System
Restore rates also scaled near 1:1 with the same effect of compression and one additional factor.
The maximum combined restore rate topped out at 90 GB/H for various numbers of drives and
compression rates.
NOTE: The test results were based on a controlled set of variables, but real-world data
compression varies from file to file. The EBS Tech Note details test variables and other factors
that can affect performance.
A formula was derived that closely approximates the backup performance for various levels of
compression. The formula was compared to actual backup and restore jobs at all tested
compression rates.
200.00
180.00
160.00
140.00
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100.00
80.00
60.00
40.00
20.00
0.00
1
1:1 Backup
Figure 4-2. Comparisons of actual compressed jobs and the formula
Backup Formula
If ((Base Rate * Compression) – (Compression
Then ((Base Rate * Compression)–(Compression
Else (43 * Drives) = Backup Rate
The Base Rate for 1:1 Backups is 15 GB/H
The Drives equal the number of DLT Drives backing up data
The Compression Loss (CL) is equal to Compression Squared
IMPORTANT: The formula can approximate backup and restore rates for the EBS, but every
backup or restore job in the real world is subject to performance variables. The formula and Sizer
Tool are only estimates, designed to be as close as possible to real world conditions.
Backup Speed vs. Compression
2
3
4
Number of DLT Drives
1.7:1 Backup
2:1 Formula
5
6
7
2:1 True
2.5:1 Backup
2
)) < 43
2
)) * Drives) = Backup Rate
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