Tandberg Data SLR7-140 PROGRAMMER, Руководство пользователя

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Tandberg Data About Tape Streamers
2-20 Tandberg SLR Product Line SCSI Functional Specifications
2.7.1.1. SLR50 Drive
The data buffer in the SLR50 Drive has been split into
two distinct partitions, a host buffer and a tape
buffer.
Host Buffer
The host buffer is used to buffer logical blocks
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.
Tape Buffer
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 the tape buffer. An optional data
compression unit may also be placed in the data path
between the two buffers.
Logi ca l Block
Logi ca l Block
Logi ca l Block
Logi ca l Block
Logi ca l Block Physica l Fra m e
Physica l Fra m e
Physica l Fra m e
SC SI Bus
M ed i um
Host Buffer Tape Buffer
D a ta
Form a tter
D a ta
C om p ressi on
Figure 2-6: 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 buffer is allocated 512 KBytes. For
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 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 host
buffer size may be somewhat less than the allocated
size.