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amount of data that is being sent. For example, to write 64 KB of data with no retry
operations, you need 64 KB read and write buffers. If you allow one retry operation, you
need only 32 KB buffers.
Using SSA Target Mode
SSA Target Mode does not attempt to manage the data transfer between devices. It
does, however, take action if buffers become full, and it ensures that read operations
can read data from only one write operation. Any protocol that is needed to manage the
communication of data must be implemented in user-supplied programs. The only
delays that can occur when data is being received are delays that are characteristics of
the SSA system and of the environment in which it operates, and delays that are
caused by full buffers.
SSA Target Mode can concurrently send data to, and receive data from, all attached
nodes. Blocking-read and blocking-write operations do nothing until data is available to
be read, or until the write operation is complete.
Execution of Target Mode Requests
The write operation transfers the data into the device buffers. When a buffer is full, the
SSA adapter starts to transfer the data to the remote using system. At the same time,
the user's application program continues to fill the device buffer with the remaining data
that is being transferred. If the amount of data that is being written is larger than the
available buffer space, the application program waits until more space becomes
available in the device buffers. As each buffer is sent, the tmssa device driver checks
whether any more data is to be sent. If more data is to be sent, the device driver
continues to send that data. If no more data is to be sent, and the write operation is in
blocking mode, the device driver starts the waiting application program. If the write
operation is in nonblocking mode, the write status is updated. If an unrecoverable error
occurs, the write operation is ended, and the remaining buffers are discarded.
The read operation transfers received data from the device buffers to your application
program. When the read operation ends, or the write operation stops sending data, the
read operation returns the number of bytes read.
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User's Guide and Maintenance Information
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