Compaq ProLiant 6000 Compaq DLT Tape Array II: High-Performance Backup of Ente - Page 20

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ECG075.0997 (cont.) DLT Tape Array II ... Data compression is an important factor in backup speeds, and in most cases, it is not something the customer can control. In investigations into real customer data set composition, it was found that most servers contain data with a compressibility between 2:1 and 4:1. The backup speed for non-compressible data highlights the advantage of the data compression hardware built into the drive: The 2:1 data backed up nearly twice as fast as data backed up with the tape drive compression feature turned off. If data set compressibility is 2:1 or greater, customers will achieve significantly faster backup speeds using the 35/70 GB DLT drive, with its built-in compression. As the data set becomes more compressible, the advantage gained is proportionally less: Some of the tests documented in this brief were run with 2:1 data compression; others were run with 4:1 compression. The performance difference between these compression levels is only about 14 percent. 40 35 30 25 GB/hr 20 15 10 5 0 15/30 1:1 2:1 15/30 Restore 4:1 8:1 35/70 35/70 Restore Figure 12: Data compression effects at various levels of compression (indicated at bases of columns). 1:1 3.90 3.93 15.35 2:1 7.51 6.97 29.50 4:1 9.68 9.35 33.32 8:1 9.99 9.80 36.13 Table 7: Test data for compressibility/performance tests. 15.39 26.46 23.07 28.64

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7
%
(cont.)
DLT Tape Array II
ECG075.0997
Data compression is an important factor in backup speeds, and in most cases, it is not
something the customer can control. In investigations into real customer data set composition, it
was found that most servers contain data with a compressibility between 2:1 and 4:1.
The backup speed for non-compressible data highlights the advantage of the data compression
hardware built into the drive: The 2:1 data backed up nearly twice as fast as data backed up
with the tape drive compression feature turned off. If data set compressibility is 2:1 or greater,
customers will achieve significantly faster backup speeds using the 35/70 GB DLT drive, with
its built-in compression. As the data set becomes more compressible, the advantage gained is
proportionally less: Some of the tests documented in this brief were run with 2:1 data
compression; others were run with 4:1 compression. The performance difference between these
compression levels is only about 14 percent.
0
5
10
15
20
25
30
35
40
1:1
2:1
4:1
8:1
GB/hr
15/30
15/30 Restore
35/70
35/70 Restore
Figure 12: Data compression effects at various levels of compression (indicated at bases of columns).
1:1
3.90
3.93
15.35
15.39
2:1
7.51
6.97
29.50
26.46
4:1
9.68
9.35
33.32
23.07
8:1
9.99
9.80
36.13
28.64
Table 7: Test data for compressibility/performance tests.
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