Quantum 1200 Series DAT Autochanger Guía de usuario descargar pdf (Pagina 227)

SDLT 600 SCSI Interface Guide Chapter 4: SCSI Commands

81-81200-02 REV A01 January 2005 4-185

4.17.1 Retrieving Diagnostic Data

The host should first send a READ BUFFER command in Descriptor mode (Mode 3) to determine

the size of the buffer being returned. In response to the READ BUFFER command, the drive returns

4 bytes of data, 3 of which contain the size of the buffer. Note that this may take a while to complete

(possibly as much as 1 minute). The host uses this data to establish the Buffer Offset and Allocation

Length fields of the CDB. Once the host knows the size of the buffer, the host sends a Mode 2

READ BUFFER command to transfer the data across the SCSI bus.

Read Data from the Saved Buffer (A1h)

The A1h buffer (the saved buffer) contains information saved from an event that caused the drive to

unexpectedly reset. Use Mode 3 to test for event data. The event data is not actually generated with

this first READ BUFFER command—instead, the size of the data is returned. Note: If the length of

this buffer is 0, an unexpected reset event has not occurred.

Read Data from the Live Buffer (A2h)

The A2h buffer (the live buffer) contains the latest information about the current state of the tape drive.

The buffer is populated each time a READ BUFFER command using Mode 3 with the A2h buffer ID

is received by the drive. The information in this buffer is most useful when an error occurred that did

not cause an unexpected reset of the drive; for example, a Hard Read Error (HRE) or a Hard Write

Error (HWE).

The buffer contains actual event data. Note that retrieving this information overwrites any other saved

event information, so it is best to check the size of the Saved Buffer first to check if there is any useful

information available (do this with a Mode 3 READ BUFFER command, described in “Descriptor

Mode (03h)” on page 4-187).

Allocation

Length

Specifies the maximum number of bytes the initiator has allocated for returning

data. The host uses this field to limit the size of data transfers to its own internal

buffer size.

Comp Compression. When set to 1, enables compression of buffer A2h (the live

buffer); when set to 0, disables compression of buffer A2h. Note: This

parameter applies only to buffer A2h, and is ignored for all other buffers.

Table 4-107. READ BUFFER Command Descriptor Block — Field Descriptions (Continued)

Field Name Description

1 2 ... 222 223 224 225 226 227 228 229 230 231 232 ... 293 294

Sin comentarios

Quantum 1200 Series DAT Autochanger Guía de usuario Pagina 227