Media
Test
RND (Random). This bit selects either random or sequential addressing.
The
media testing
begins with the logical block address specified
in
the CDB.
If
RND is set to zero (0),
the
test
proceeds sequentially from the specified logical block. Logical block zero follows
the
last
logical block on the media when using sequential addressing.
If
RND is set
to
one (1),
the
next address is generated randomly from any block on the media.
RST (Reset Seed). This bit is used only when RND is set
to
ope (1). When RST is set
to
one (1), the Target initializes its random number seed using
the
specified block address. This
capability provides a method
to
enable a repeatable sequence of random addresses for pairs of
MEDIA
TEST
commands (i.e., a write followed by a read).
If
RND is set
to
one (1) and RST
is set
to
zero (0), the random number seed is not reset.
If
RND is set
to
zero (0), RST must
also be set
to
zero (0).
Address. This field specifies the media test area; refer
to
the previous explanation for
the
PHYS bit.
Transfer Length. This field indicates the number of blocks
to
be
tested, unless terminated
by an error. An unrecoverable error terminates the MEDIA
TEST
command and generates
CHECK CONDITION
status
with the appropriate sense information.
If
only recoverable
errors occur, the media test will run
to
completion and return a CHECK CONDITION
status
with sense information set for the last recoverable error which occurred. Information on any
additional errors can be obtained from
the
drive error log. A transfer length of zero shall not
cause any media transfer to occur and shall not be considered
an
error.
On a sequential media test, if the Transfer Length is greater
than
the length remaining from
the
start
address
to
the
maximum block address, the test will continue
to
run
from address
zero
(0) after
the
maximum block address is reached. This is not considered
an
error. This
"wrap around" may occur more
than
once during a long test.
For random tests, only single block operations are performed. The transfer length field
indicates the number of these operations to
be
performed.
DRAFT
Vendor
Unique
Command
Descriptions
B·17
1/18/93
09:58
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