topic Re: Compressed Tape Check in Operating System - HP-UX

Compressed Tape Check

Henry_52 — Wed, 04 Aug 2004 13:46:18 GMT

I backed up files using Data Protector.
Tape Cartridge is LTO Ultrium.(up to 200GB compression, 100GB uncompressed.)
Total data is over 300GB uncompressed.
How can I check actual compressed Total size in the Tape Cartridge using unix command ?

Best Regards,

Henry

Re: Compressed Tape Check

Pete Randall — Wed, 04 Aug 2004 13:51:15 GMT

Henry,

Check DP's "devices and media" report for that particular media.

Pete

Re: Compressed Tape Check

Henry_52 — Wed, 04 Aug 2004 14:09:06 GMT

Hi Pete,

I imported and scaned several tapes and
checked devices tab and media tab to
check total size. some tape's size is same
but some tape is different.
I want to know actual compressed and uncompressed size.
Please let me know about this.

Best Regards,

Henry

Re: Compressed Tape Check

A. Clay Stephenson — Wed, 04 Aug 2004 22:36:14 GMT

All you can really know is how much uncompressed data was written to the media; if you think about it for a moment you will realize that the only thing that the host computer can possibly know it how many bytes it wrote to the device. In fact, OB2/DP will write to end of media -- as reported by the device itself -- rather than stopping at whatever size that you initialized the media.

The 200GB compressed / 100GB uncompressed value assumes a 2:1 compression ratio. How much real world data do you think actually compresses exactly 2:1? You will find that some data compress barely at all while other data compress at much higher ratios.