Quantum LTO 4, User Manual

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SCSI Interface Overview Page 19
the tape with different block sizes in the fixed mode. Also, the host may change the
block size after BOM, allowing on-the-fly block-size changes.
The READ command Fixed bit also specifies fixed or variable mode. When reading
in variable mode, the host must know the size of the block to be read from the tape
in advance in order to avoid causing the LTO drive to return a Check Condition with
Incorrect Length indicated in the Sense data (ILI). Also, the data transfer may be
truncated (cut off) when the recorded block does not match the transfer length in
variable mode or the current block size in fixed mode.
The READ command includes a SILI bit to Suppress ILI Check conditions.
When the SILI bit is set, the host usually specifies the maximum block size before
reading so that the data blocks are not truncated, and no Check Conditions are
generated.
The SCSI READ BLOCK LIMITS command returns the minimum and maximum
block sizes that the LTO drive can support. The Block Limits data is not modified to
reflect the current mode of writing—fixed or variable. The Block Limits returned data
is not modified to reflect the current block size for the next fixed-mode WRITE. The
MODE SENSE command is used for that purpose.
2.7.10 Library Features
The library (automation device) controls automation-related operations of the LTO
drive via the ADC device server presented on the ADT port. For configuration in
manufacturing, some of these features can be controlled via two vendor-specific
mode pages implemented by the SSC device server and addressed through the
primary port.
2.7.10.1 Auto Unload Mode
The LTO drive has an Auto Unload Mode that may be accessed via a Mode
command to Mode Page 21h. The purpose of the Auto Unload mode is to allow the
drive to be configured to work in Library systems or as a Stand Alone drive. The
Auto Unload mode allows the drive to control how the tape is unloaded in
“automatic” type situations. There are four Auto Unload modes that are possible.
•
Do Nothing – Stay threaded at BOM (mode 0).
•
Unthread Only (mode 1).
•
Unthread and unload (mode 2).
•
Unthread and unload non-data cartridges, data cartridges go to BOM (mode 3).
Basically data cartridges behave as for mode 0 and non-data cartridges behave
according to mode 2.
•
Unthread and unload non-data cartridges except expired cleaning cartridge
remain seated (mode 4). Data cartridges are threaded to BOM.
Following are the possible “automatic” situations where the ejection process will be
controlled using the Auto Unload mode. As shown in the list below, this covers not