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Ultrium 960 - LTO3 Compression scheme

Samuel Nair
Occasional Visitor

Ultrium 960 - LTO3 Compression scheme


I have noticed a few instances where the hardware compression system on the drives seem to fail(almost zero compression).

I filled up the free space on a 80GB HDD with zero's using a quick dd. Following which i wrote an 80GB file of the HDD using a dd(dd if=/dev/hda of=dump.hda).

I dumped this file to the tape with a tar command using 128K blocks, hardware compression was turned on. It used 610813 blocks on tape. i.e on tape compressed size = 610813*128 = ~74.5GB

Following this i ran gzip on the same 80GB file and ended up a 15GB gzipped file.

From reading through some docs on wikipedia apparently the compression of data is often turned off automatically if the drive determines that the data is already highly compressed. How does it make this determination...? Can you include some details about the kind of compression algorithm used on the HP Ultruim 960 drive.

Occasional Advisor

Re: Ultrium 960 - LTO3 Compression scheme

Hi Sam

You might want to look at this document.

It is about Data Compression. This should answer the questions that you have.