-Hardware compression is detected by measuring the writing speed difference of the tape drive when writing an amount of compressable and uncompresseable data\. It does not rely on the status bits of the tape drive or the OS parameters\. If your tape drive has very large buffers or is very fast, the program could fail to detect hardware compression status reliably\.
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-During the first pass, it writes files that are estimated to be 1% of the expected tape capacity\. It gets the expected capacity from the \-e command line flag, or defaults to 1 GByte\. In a perfect world (which means there is zero chance of this happening with tapes :\-), there would be 100 files and 100 file marks\.
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-During the second pass, the file size is cut in half\. In that same fairyland world, this means 200 files and 200 file marks\.
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-In both passes the total amount of data written is summed as well as the number of file marks written\. At the end of the second pass, quoting from the code:
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-* Compute the size of a filemark as the difference in data written between pass 1 and pass 2 divided by the difference in number of file marks written between pass 1 and pass 2\. \.\.\. *
+If the device cannot reliably report its comprssion status (and as of this writing, no devices can do so), hardware compression is detected by measuring the writing speed difference of the tape drive when writing an amount of compressable and uncompresseable data\&. If your tape drive has very large buffers or is very fast, the program could fail to detect hardware compression status reliably\&.