SUMMARY: compression ratios on exabyte drives

From: Ayrton Sargusingh (
Date: Tue May 30 1995 - 14:50:36 CDT

Problem Description
I was achieving only 6.33GB on a 112 metre tape using the 5GB 8505
with compression (rated at 10GB). The ratio is closer to 5:3 rather
than 2:1. Is that typical?

System Configuration
Sun SPARC 20, Solaris 1.2, 8505 and 8505XL drives.
112 metre and 160 metre 8mm data cartridges.

Thanks to all those who responded. The consensus was that 2:1 compression
ratios may be achieved if a large percentage of files being compressed
are text-based. The ratios will vary greatly from site to site depending
on the type of data being archived. In my case, since there are many
compressed files and binaries in the mix, a 5:3 ratio may be more typical.

Follow-up Question
Andy Feldt reminded me of a discussion I had with Sun concerning the 8505XL
drive and the 160m tape. The dump command that I use for both drives is:

        dump 0ubdsf 126 54000 13000 /dev/rst24

I was told that the same arguments applied whether I am using a 8505 with
the 112 metre tapes or a 8505XL with the 160 metre tapes. Can someone
validate this?

Ayrton Sargusingh, SBR System Manager, RSD | phone: 613-998-2932
Defence Research Establishment Ottawa (DREO) | fax: 613-998-4560
3701 Carling Ave., Ottawa ON, Canada K1A 0Z4 | email:

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