Sony Tape Drive Compression

This group appears more suited to this question than comp.compression...

I have a Sony AIT-2 SCSI tape drive using 50/120 GB tapes and Retrospect
Backup 6.0. Sony's compression ratio is advertised as 2.6. The maximum I've
ever gotten on a tape using hardware compression is around 57 GB.

I realize compression is dependent on file type, and I am backup up a mix of
non-compressed and compressed files. But, out of curiosity, what have others
seen using this drive? Using a backup of an operating system drive (w/ no
user data) as a reference may make comparison easier.

Thanks,

--
Yoann Roman

On 2006-10-11, Yoann Roman wrote:
This group appears more suited to this question than comp.compression...

I have a Sony AIT-2 SCSI tape drive using 50/120 GB tapes and Retrospect
Backup 6.0. Sony's compression ratio is advertised as 2.6. The maximum I've
ever gotten on a tape using hardware compression is around 57 GB.

I realize compression is dependent on file type, and I am backup up a mix of
non-compressed and compressed files. But, out of curiosity, what have others
seen using this drive? Using a backup of an operating system drive (w/ no
user data) as a reference may make comparison easier.

Conventional wisdom is that Sony's claims of 2.6x compression for AIT are
based on compressing a stream generated by 'cat /dev/zero'. I've never
seen anywhere near 2x.

--
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University

I've also seen indications that when Sony OEMs AIT drives to others
such as Compaq that the firmware uses a different compression
algorithm, described as "the more reliable 2:1"

I had some tapes that I believe were in this 2:1 format a while back,
and my Sony drive couldn't read them, but a Compaq drive could. (These
were AIT3's)

Has anyone out there had any similar experiences?

Chris

"Yoann Roman" writes:
I have a Sony AIT-2 SCSI tape drive using 50/120 GB tapes and Retrospect
Backup 6.0. Sony's compression ratio is advertised as 2.6. The maximum I've
ever gotten on a tape using hardware compression is around 57 GB.

I have an AIT-1 (same compression algorithm). On a 35 GB tape, I typically
get 45-50 GB of backups, so roughly 1.3:1. This is on my home systems, so
a fair amount (50%?) of the data is compressed audio or images.

Anton