Setting up the tape
Before you can run the data dump, you have to inform the program which drive and medium it should save to using the "Streamer-> Tape - Prepare" menu:
The media setup window
Before a tape (medium) can be used with Z-DATdump, it has to be set up. A name for the tape and the correct tape size must be entered. The process is started with a click on the button Prepare and takes a few minutes.
The displayed tape capacity:
Manufacturers usually specify two capacities for their tapes: the native capacity and the compressed capacity.
Native Capacity: This capacity indicates how much data one can approximately store on the tape without using the hardware compression of the tape drive. (e.g. for LTO-6 tapes the native capacity specified is 2.5 TB)
Compressed capacity: This capacity indicates how much data one can approximately store on the tape with activated hardware compression assuming that the data can be compressed in the ration 2:1 or 2.5:1. (e.g. for LTO-6 tapes the compressed capacity specified is 6.25 TB)
The compression ratio achived depends on how good the files can be compressed and is often lower in real situations.
Why is the displayed capacity higher than the one specified by the manufacturer?
Tapes are usually manufactured a few meters longer than what would be needed to achive the capacity specified by the manufacturer. Due to the wear of the tape throughout its life time bad blocks form on the tape which can't be used to store data anymore. To assure that the tape meets its specified capacity throughout its guaranteed life cycle the tapes are made a bit long to start with. Z-DATdump gets the tape capacity delivered from the tape drive and therefore displays the amount of data that could be actually stored on the whole length of the tape. (e.g. for an LTO-6 tape the displayed capacity can be 2.62 TB instead of 2.5 TB)
GB and GiB / TB amd TiB:
Z-DATdump displays the tape capacity in Gigabyte (GB) or Terabyte (TB) and in Gibibyte (GiB) or Tebibyte (TiB). The values of Mega-, Giga-, and Terabyte etc. are calculated using powers of 10 as a base, in other words a Kilobyte is defined as 1000 Bytes. The values of Megi-, Gibi- and Tebibytes etc. are calculated using powers of 2 as a base, in other words a Kibibyte is defined as 1024 Bytes. Manufacturers use Mega-, Giga- and Terabyte etc. to specify the capacity of their tapes.
More information on this topic can be found on Wikipedia.
Peparing the tape
With the "prepare" button, the medium info is written to the tape header; no formatting is needing. The tape specifications are automatically saved by Z-DATdump and are, for example, used by the tape-auto-format function to automatically prepare empty tapes.
Warning: all data on the medium is deleted and cannot be recovered!
Manual tape size
If there is no predefined item for your medium, you can manually enter the tape size.
Consider tape compression
If you want to use the compressed capacity (2:1 or 2,5:1 compression) of the medium, you can set this option. For this to work, your drive must support hardware compression and Z-DATdump must recognize it. If the option "Use tape compression" is activated during tape setup, the compressed capacity of the tape as reported by the tape drive is stored as the maximum size of the tape. Z-DATdump can not check whether this capacity is actually available on the tape (there might be defective tape sectors etc.).
Don't activate for multispanning: If you plan on using this tape for multispanning you mustn't activate this option. To use a tape for multispanning it has to be setup with its native capacity.
Alot of file formats on modern computers already use compression, for example most multimedia files (e.g. MP3, MP4, JPG, AVI, even DOCX). Those files usually don't yield good compression rates when they are compressed a second time . A tape compression factor of 1.1:1 or 1.2:1 is therefore more realistic than the one mentioned by the tape manufacturer. This is just enough to compensate for the capacity loss caused by defective tape sectors ("drops").
The tape setup should therefore most of the time be done with the native capacity reported by the hardware. The "Use tape compression" option should only be used when backing up pure text files, databases or if you specificly know that the data you're going to backup can be compressed well.
The professional version of Z-DATdump can save a maximum of 384,000 or unlimited* many files (depending on whether the file list is created in RAM or on the hard disc). The free version saves at most 65,536 files with a total size of no more than 12 GB per tape.
* only limited by the tape, computer and operating system
Z-DATdump is a program by Andreas Baumann © 2008 - 2017.
All used trademarks and company names are subject to copyright of their respective companies.