HP Data Protector Software Performance White Paper

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Figure 37 shows the different ratios for software and hardware compression. HP-UX gzip (GNU
zip) was additionally tested because it is the current standard compression utility for UNIX and a
good indicator for possible ratios. The compression ratio of HP-UX gzip resulted in 59%, the
Ultrium 960 built-in compression in 50% and Data Protector software compression in 45%.
Figure 37. Compression ratios for HP-UX
There are some reasons why Data Protector’s software compression ratio was lower:
1. The Data Protector compression is based on the Lempel-Ziv compression algorithm which is
less space-efficient than for instance the newer gzip compression utility. On the other hand,
better compression has its price in terms of speed.
2. gzip offers different compression levels – between less and best compression. This test was
executed with the default level, which is biased towards high compression at expense of
speed.
3. Ultrium tape drives use the Advanced Lossless Data Compression (ALDC) algorithm for data
compression. ALDC is an implementation of the Lempel-Ziv method of compressing data
and can be implemented in hardware very efficiently. ALDC has the ability to switch into a
non-compressed mode according to the structure of the data pattern. This means that highly
random data does not actually expand when compressed. This method of compression is
very fast and space-efficient at the same time.
IDB logging level
The logging level determines the amount of detail on files and directories that is written to the
IDB during backup, object copying, or object consolidation. Regardless of the logging level, the
backed up data can always be restored. Data Protector provides four logging levels: Log All,
Log Directories, Log Files, and No Log. The different logging level settings influence the IDB
growth, backup speed, and the convenience of browsing data for restore. Since the impact is
mostly relevant for the Cell Manager which is not focus of this white paper, it was not tested.
Note: Any Data Protector test was executed with the default configuration parameter Log All
which represents the worst case in terms of performance.
Compression Ratios for Typical Files (2:1)
59%
51%
46%
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
Data Protector
Compression ON
Ultrium 960 Built-In
Compression
HP-UX gzip (default
parameters)
Compression Ratio