ntbackup compressione

[CA1268492]

Salve,
ho un server Proliant ml370 G3 windows 2003 con in Ait 35 scsi che deve fare il backup su nastro di 39GB di dati.
Con il comando ntbackup ed un file .bks ho schedulato il backup notturno ma non mi basta un nastro anche se la cassetta potrebbe avere la compressione 2:1, in più ho fatto dei test con un diagnostico che mi ha confermato che la compressione del nastro funziona.
Abbiamo anche sostituito l'Ait ma continua a dare il solito problema.
I dati da salvare sono i classici file doc xls ppt jpg ecc...
Avete qualche succerimento?

[Robert-Jan Goossens]

Daniele,

Please post your question in English.

The compression ratio depends all kind of variables, kind of files, hardware compression <--> software compression, Iâ ve seen compression ratios of 4:1 on database files and less then one on zipped/compressed files.

Below is from the quantum tech database.

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What data compression technique is used and will it be used consistently for all input data? For example, can it be used with files that are already compressed?

All DLT tape drives use LZ1, a variant of the Lempel-Ziv compression algorithm. LZ1 was selected over IBM's IDRC because testing indicated that LZ1 provided higher compression and better efficiency.
Though the DLT compression is specified as a 2 to 1 ratio, compression can vary depending on the input data. Binary files may compress at a 1.5 to 1 ratio while images from a Paint application may compress at a 4.5 to 1 ratio. There may be no compression at all with data that has already been compressed with a Lempel-Ziv or more powerful compression method. Such compressed data, or very random data (including encrypted data), will likely expand by about 5%. IDRC compressed data usually gets compressed slightly more by LZ1.
The only disadvantage to using compression all the time is that some files may expand slightly, as noted above. If in doubt, and if there is a significant amount of data, the Log Sense Read/Write Compression Ratio page can be used to monitor the compression rates that are actually achieved.
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Hope this helps,
Robert-