5190/5194 Modular Tape Subsystem Manual

Operating the Cartridge Tape Drive and ACL
5190/5194 Modular Tape Subsystem Manual—426878-002
4-55
Running in Buffered Mode
•
SETMODE 99 sets the buffering mode of the 3216 controller with the modular tape
subsystem. Changing the buffering mode can affect system performance and error
reporting. See Running in Buffered Mode on page 4-55.
•
SETMODE 119 sets the tape mode. The 5190 and 5194 drives currently support
only one tape mode setting:
•
SETMODE 162 sets the compression mode (5190 tape drive only):
Changes to compression using SETMODE 162 are allowed only at the beginning-
of-tape (BOT) mark. Otherwise, the 5190 tape drive returns an error.
For more information about the SETMODE procedure call, see the Guardian
Procedure Calls Reference Manual and the Guardian Programmer’s Guide.
Running in Buffered Mode
Running a streaming drive in buffered mode improves performance over nonbuffered
mode, depending on the size of the files involved. File buffering, however, affects error
reporting. If the buffering mode is not explicitly set by an application, the tape process
disables buffering by default, resulting in record-level recovery. When record-level
recovery is used, the application is notified of an I/O completion as soon as the data
resides on the tape. An error is returned if the data was not successfully written.
How Buffering Affects Error Reporting
When buffering data (file-level recovery), the tape process and the tape drive allocate
storage for multiple records and return I/O completion to the application immediately. If
an error occurs while the drive writes data to tape, the application is notified during a
subsequent I/O operation. When the application attempts to write a file mark
(CONTROL 2), all buffered data is flushed to the tape and any errors encountered are
returned as the result of the CONTROL operation. Thus, an application can never
know which record was written incorrectly to tape—only that an error occurred.
When buffering data and file marks (reel-level recovery), data and file marks are stored
in temporary buffers. To guarantee that data has successfully been written to tape,
Setting param1 Value
Buffering off (record-level recovery) 0
Buffer data (file-level recovery) 1
Buffer file marks (reel-level recovery) 2
Setting param1 Value
Set tape mode to default streaming speed 1
Setting param1 Value
No data compression 1
Data compression (IDRC) 2