Reference Guide

Chapter 4 SCSI Commands
READ ATTRIBUTE Command (8Ch)
DLT-S4 Interface Reference Guide 261
• Super DLTtape media does not require that attributes be written
(using the
WRITE ATTRIBUTE command) in ascending order. The
attributes that can be written are independent of one another and can
be written in any order.
• Since EMAM is written to the tape, there is always a short window
during which the tape is loaded but the attributes have not been read
from the tape and stored in RAM. If, during this brief span of time,
the drive receives a
READ ATTRIBUTE or WRITE ATTRIBUTE
command, it responds with the Sense Key set to NOT READY, and the
Additional Sense Code set to
LOGICAL UNIT NOT READY, MAM NOT
AVAILABLE
. The application should retry the command in this case.
A Comparison of MAM
and EMAM
4
The tape drive incorporates a new feature called Enhanced Medium
Auxiliary Memory (EMAM). This feature is used to store MAM attributes
in a log file on the tape itself. The attributes are accessed using the
READ
ATTRIBUTE
and WRITE ATTRIBUTE commands. An EMAM device mimics
a MAM device, with the following exceptions:
• If the tape is bulk erased, the EMAM attribute data is lost. The next
time the tape is used, it has default values in the attribute fields.
• Since the EMAM data is read off the tape, the host needs to wait for
one of two ready states to read and write attributes. If the DLT-S4
tape drive is configured to report the MAM Available Unit Attention
using the EEPROM setting “RepMAMAvailUA” (see table 87
on
page 151), once that UA is reported to the host, it can read and write
MAM attributes.
If the DLT-S4 tape drive is not configured to report the MAM
Available Unit Attention, the host needs to wait for the Not Ready to
Ready transition prior to reading and writing MAM attributes. If the
host sends
READ ATTRIBUTE or WRITE ATTRIBUTE commands prior
to the Ready state, the drive returns a
CHECK CONDITION status. The
Sense Data is set to
NOT READY, the Sense Key is set to LOGICAL UNIT
NOT READY
, and the Additional Sense Code is set to MAM NOT
AVAILABLE
.