Figure 2-6: The Slr50 Buffer System (Write Mode) - Tandberg Data SLR7-140 PROGRAMMER Manual

Host Buffer
Tape Buffer
Hos t Buf f er
SC SI Bus
Figure 2-6:
Tandberg Data
2.7.1.1. SLR50 Drive
The data buffer in the SLR50 Drive has been split into
two distinct
buffer.
The host buffer
transferred at high-speed (up to 20 MBytes/s) to/from
the SCSI interface. Notice that only data are buffered
in the host buffers. Tapemarks do not occupy any space
in the host buffer. Tapemarks do however consume other
resources in the buffers system so there is an upper
limit to the number of tapemarks that the buffer system
is able to hold.
The tape buffer is used to buffer formatted physical
blocks going to/from the recording medium. The data in
the tape buffer is transferred to/from the media at
speeds varying from up to 2 MBytes/s (SLRtape50 medium)
down to 480 KBytes/s (DC9250 medium).
A data formatting unit sits in the data path between the
host buffer and
compression unit may also be placed in the data path
between the two buffers.
Logi cal Bl ock
Logi cal Bl ock
Logi cal Bl ock
Logi cal Bl ock
Logi cal Bl ock
The SLR50 Buffer System (Write Mode)
In a SLR50 Drive equipped with a 1 MByte physical data
buffer the host buffer will occupy about 450 KBytes
while the tape
drives equipped with a 2 MByte physical data buffer the
host buffer will occupy about 1450 KBytes while the tape
buffer is allocated 512 KBytes.
Note that the use of the host buffer is optimized so
that as long as most logical blocks are of the same size
the complete
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 host
buffer size may be somewhat less than the allocated
size.
2-20 Tandberg SLR Product Line SCSI Functional Specifications
partitions, a host
is used to
the tape buffer.
D at a
For m at t er
D at a
C om pr es s i on
buffer is allocated
allocated size
About Tape Streamers
buffer and
buffer logical
An optional
Tape Buf f er
Phys i cal Fr am e
Phys i cal Fr am e
Phys i cal Fr am e
512 KBytes.
for the host buffer
a tape
blocks
data
M edi um
For
is