Product

Platform

Operating system

Error

Symptoms

In Media Manager, the used space of the tape is always so much less than the tape capacity. For e.g. an AIT-3 tape, on the cartridge, it shows 260Gb compressed and 100Gb uncompressed, however, when the archiver tape is full, it usually only archives up to around 100Gb, not as close as 260Gb.

Cause

Solution

The AIT-3 native (i.e. uncompressed) capacity is 100 GB. The compression ratio that can be achieved is completely data dependent, so highly random (e.g. already compressed data) do not compress further and may even expand.

For example, try putting a couple of ZIP-files into another ZIP-file and see what the compression ration is there. Sony use a 2.6:1 compression ratio (other tape technologies, like DLT use 2:1 as a typical ratio).

The archiver uses the hardware compression of the tape drive, so when an AIT-3 tape is "full" with only 110 GB of data, it really is full. We have seen compression ratios at customer sites range from almost none (e.g. 1.1:1) up to about 2:1, but typical values appear to be 1.4:1 with files of the type our customers process

Permanent fix:

See also

Keywords

archiver - Media Manager, archiver FAQs

Technical contact(s)

Amy Chan

Submitted by

Amy Chan

Date submitted

16 June 2006