Tape Cartridge Densities and Compression
Changing the Density and Compression for Writing
4-3
*compressed capacities assume a 2:1 compression ratio
Note
You can appear to set any density with any tape cartridge on the front
panel. However, if the combination of density and tape cartridge is invalid,
as shown in the tables above, the density will switch back to the default
density and compression settings as soon as the drive starts writing.
The drive cannot provide compression at 2.6 GB or 6.0 GB densities. If you
need to use compression at these densities, use a backup application that
provides software compression. This compresses the data before sending it
to the drive, instead of the drive compressing the data when it receives it.
Software compression is slower than using the drive’s hardware
compression facility, but it can be equally effective in terms of capacity.
How to Select Density and Compression
Note
Always use the default density (and compression setting) of the tape
cartridge unless you want to write a tape cartridge at a different density
so that it can be read in a lower capacity DLT drive. This will allow you to
store the maximum amount of data on the tape cartridge.
Density and compression changes take effect only when the drive starts
writing at Beginning of Tape. This means that a tape can only ever be
written at one density—entirely with or without compression.
The time you are most likely to want to select the density at which the tape
cartridge is written is immediately after loading the tape cartridge. You can
however select the density at other times.
• With DLTtape IV cartridges, you can select only 20.0, 35.0 or 40.0 GB
densities and choose to have compression on or off. If you try to select
another density, the setting will change back to the default density
(40 GB) as soon as the drive starts writing to tape.
• With DLTtape IIIxt cartridges, you can only choose to have compression
on or off. Any density setting other than 15.0 GB will automatically
default back to 15.0 GB when the drive starts writing to tape.
Density Setting
10.0/15.0 GB
20.0 GB
35.0 GB
40.0 GB
Tape
Native
Compress’d Native Compress’d Native Compress’d Native Compress’d
Type III
10.0 GB
20 GB*
No
No
No
No
No
No
DLTtape IIIxt
15.0 GB
30 GB*
No
No
No
No
No
No
DLTtape IV
No
No
20.0 GB
40 GB*
35.0 GB
70 GB*
40.0 GB
80 GB*
dlt-m.book Page 3 Thursday, May 4, 2000 3:52 PM
