Tandberg Data
About Tape Streamers
2-21
Tandberg SLR Product Line SCSI Functional Specifications
2.7.1.2.
SLR7, SLR60, SLR75, SLR100 and SLR140 Drives
The data buffer in the SLR7, SLR60, SLR75, SLR100 and
SLR140 Drives consists of a single logical unit with a
size of nearly 8 MByte.
Data Buffer
The data buffer is used to buffer data from logical
blocks transferred at high-speed (up to 40 MBytes/s)
to/from the SCSI interface. When moved into the buffer
the data is first compressed and then formatted into
frames of physical blocks. The data in the data buffer
is then transferred to/from the media at speeds varying
from up to 6 MBytes/s (SLR140) down to 3 Mbytes/s
(SLR7).
Logi
cal
Bl
ock
Logi
cal
Bl
ock
Physi
ca l
Fra m e
Physi
ca l
Fra m e
Physi
ca l
Fra m e
SC SI Bus
M ed i
um
D ata Buffer
D a ta
Form a tter
D a ta
C om p ressi
on
Logi
ca l
to Physica l
M a p p ing
Figure 2-7: The SLR140, SLR100, SLR75, SLR60 and SLR7 Buffer System (Write
Mode)
Note that the use of the buffer is optimized so that as
long as most logical blocks are of the same size the
complete allocated size for the host buffer is utilized
to buffer data. When mixing blocks of different sizes or
when a very large number of tapemarks are flowing
through the buffer system, the effective buffer size may
be somewhat less than the physical size.
2.7.2.
Data Formatting
When data are moved from the host buffer to the tape
buffer it is grouped into physical blocks. The physical
blocks are again grouped into frames. In addition to
host related data and tapemarks the frames hold addi-
tional information like error correction codes (ECC) [9]
- [17].
The size of the physical block as well as the number of
blocks per frame depend on the tape format used [9] –
[17].
The tape buffer is used to buffer complete frames. The
maximum number of frames depends on the tape format in
use. With an SLR32 medium for example, the tape buffer
is able to hold up to 16 frames each holding a maximum
