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тАО12-15-2004 06:58 AM
тАО12-15-2004 06:58 AM
9840B compression
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тАО12-15-2004 07:07 AM
тАО12-15-2004 07:07 AM
Re: 9840B compression
I don't think there is a way to find the compression beforehand. It depends on the type of media used, the type of data you are copying and the device file you are using. Use of /dev/rmt/*BEST* devices normally give you the best compression.
Hope this helps.
Regds
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тАО12-15-2004 07:07 AM
тАО12-15-2004 07:07 AM
Re: 9840B compression
No, this is not possible. Compression ratio is highly data dependant and it is not possible to predict the ratio before the data is wtitten to the media.
I don't know which compression algoritm your drive use but, if LZW you can get an idea about compression ratio if you try compress or gzip on some of the data files.
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тАО12-15-2004 07:10 AM
тАО12-15-2004 07:10 AM
Re: 9840B compression
Maybe this doc will help,
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50244
Hope this helps.
Regds
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тАО12-15-2004 07:13 AM
тАО12-15-2004 07:13 AM
Re: 9840B compression
For example, suppose a 100MB file named "mydata" consisted entirely of "X's"; that would compress greatly. Now suppose that this very same file were updated with random data; the same 100MB file would not compress at all. Yet both are 100MB files.
In short, the only value that you can absolutely depend upon is the native capacity of the medium less any formatting/metadata overhead required by your backup software.
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тАО12-15-2004 07:21 AM
тАО12-15-2004 07:21 AM
Re: 9840B compression
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тАО12-15-2004 07:25 AM
тАО12-15-2004 07:25 AM
Re: 9840B compression
For some tape devices
mt -f /dev/rmt/xxx status will also help.
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тАО12-15-2004 07:30 AM
тАО12-15-2004 07:30 AM
Re: 9840B compression
I am trying to compare 9840B driver performance to the stated performance. Per spec this drive is rated at 19MB/sec native and upto 70MB/sec compressed. I am getting around 30MB/sec with NB.