The following options are available only if the TurboSTORE/iX
II product is purchased.
In addition to all of the STORE options, the following additional
options are available with TurboSTORE/iX II. For more information
on purchasing TurboSTORE/iX II, contact your Hewlett-Packard sales
representative.
Compressing Data (COMPRESS) |
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With TurboSTORE/iX II (and TurboSTORE/iX 7x24 True-Online
Backup), backup performance can be improved through the use of host
data compression. By specifying the COMPRESS parameter, the host system filters the data through
a compression algorithm prior to writing it to the backup device.
This operation has two effects:
The device's throughput
is increased by transferring more data than the device's maximum
sustained rate. The increase is dependent upon available CPU resources.
Fewer media changes are required by putting more
data on each piece of media.
Two levels of compression are supported by the COMPRESS parameter: HIGH and LOW.
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 | NOTE: No matter whether you specify HIGH or LOW, the actual level of data compression is dependent
upon the type of data being compressed. For example, program files
will not compress as much as data files. |
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You must determine which of the compression algorithms best
suits your needs. In some cases the low-compression algorithm may
perform almost as well as, or better than, the high-compression
algorithm.
It is advisable to try both algorithms on your data in order
to evaluate which algorithm best suits your needs. Some of the factors
to consider are:
Amount of CPU time required.
Amount of media required.
Be advised that when performing backups with the high-compression
algorithm, the backup can consume much or most of the processing
capabilities of the machine. The exact amount of system resources
consumed depends on your system speed and multi-processor configuration.
Using the low-compression algorithm demands less system resources,
so it is easier for other activity to coexist with the backup.
Use the high-compression algorithm if backup time is dedicated
or if the difference in the amount of media used for backup is substantial
enough to warrant the complete consumption of the machine.
When compressed format files are restored, RESTORE automatically recognizes the compressed format
and restores the files properly.
To compress data when storing files to backup, use the FILE command, then use the COMPRESS parameter in your STORE command. For example:
:STORE @.OPERATOR.SYS;*T;COMPRESS=HIGH
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 | WARNING! If you are using a backup device that performs hardware
data compression, COMPRESS=HIGH should NOT be used. Performing compression twice
is redundant, and in some cases can lead to slower backup performance.
The best throughput results occurs when using no compression or COMPRESS=LOW with hardware compressing devices. |
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