Dell PowerVault TL4000 SCSI Reference Guide - Page 68

Element, Status, Header, Sub-header, Descriptor

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DVCID: If the DVCID bit is set the media changer will return device identifiers for the Data Transfer element. A DVCID bit of zero specifies that the device shall not return device identifiers. Allocation Length: This field specifies the number of bytes that the initiator has allocated for returned data. Note that the Read Element Status command can be issued with an Allocation Length specified as 8 bytes (the length of the status page header) to determine the Allocation Length required to transfer all of the element status data that become available as a result of the command. Element Status Data Data returned by the Read Element Status command is described below. The Element Status Data consists of an 8-byte Header followed by one or more status pages (for each element type). The status pages are made up of an 8-byte sub-header and one or more element descriptors (one for each element address). Header The data returned on a Read Element Status command always starts with the Header. This Header reports the first element address, the number of elements, and the byte count of the report. Bit 7 6 5 4 3 2 1 0 Byte 0 - 1 First Element Address Reported 2 - 3 Number of Elements Available 4 Reserved 5 - 7 Byte Count of Report Available Field descriptions: First Element Address Reported: This field indicates the element address of the element with the smallest element address found to meet the Read Element Status command's request. Number of Elements Available: This field indicates the number of elements found. The status for these elements is returned if the Allocation Length specified in the Read Element Status command's CDB was sufficient. Byte Count of Report Available: This field indicates the number of available element status bytes that meet the CDB requirements. This value does not adjust to match the Allocation Length field of the CDB and does not include the 8 byte element status header. Element Status Page (Sub-header and Element Descriptor) The Element Status Page includes an 8-byte sub-header and one or more element descriptors. The sub-header includes the element type code, the settings for PVolTag and AVolTag, the length of each descriptor block, and the number of bytes of descriptor information that follow the header for the element. Bit 7 6 5 4 3 2 1 0 Byte 0 Element Type Code 1 PvolTag AvolTag Reserved 2 - 3 Element Descriptor Length 3-54 TL2000 and TL4000 SCSI Reference

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DVCID:
If
the
DVCID
bit
is
set
the
media
changer
will
return
device
identifiers
for
the
Data
Transfer
element.
A
DVCID
bit
of
zero
specifies
that
the
device
shall
not
return
device
identifiers.
Allocation
Length:
This
field
specifies
the
number
of
bytes
that
the
initiator
has
allocated
for
returned
data.
Note
that
the
Read
Element
Status
command
can
be
issued
with
an
Allocation
Length
specified
as
8
bytes
(the
length
of
the
status
page
header)
to
determine
the
Allocation
Length
required
to
transfer
all
of
the
element
status
data
that
become
available
as
a
result
of
the
command.
Element
Status
Data
Data
returned
by
the
Read
Element
Status
command
is
described
below.
The
Element
Status
Data
consists
of
an
8-byte
Header
followed
by
one
or
more
status
pages
(for
each
element
type).
The
status
pages
are
made
up
of
an
8-byte
sub-header
and
one
or
more
element
descriptors
(one
for
each
element
address).
Header
The
data
returned
on
a
Read
Element
Status
command
always
starts
with
the
Header.
This
Header
reports
the
first
element
address,
the
number
of
elements,
and
the
byte
count
of
the
report.
Bit
7
6
5
4
3
2
1
0
Byte
0
-
1
First
Element
Address
Reported
2
-
3
Number
of
Elements
Available
4
Reserved
5
-
7
Byte
Count
of
Report
Available
Field
descriptions:
First
Element
Address
Reported:
This
field
indicates
the
element
address
of
the
element
with
the
smallest
element
address
found
to
meet
the
Read
Element
Status
command's
request.
Number
of
Elements
Available:
This
field
indicates
the
number
of
elements
found.
The
status
for
these
elements
is
returned
if
the
Allocation
Length
specified
in
the
Read
Element
Status
command's
CDB
was
sufficient.
Byte
Count
of
Report
Available:
This
field
indicates
the
number
of
available
element
status
bytes
that
meet
the
CDB
requirements.
This
value
does
not
adjust
to
match
the
Allocation
Length
field
of
the
CDB
and
does
not
include
the
8
byte
element
status
header.
Element
Status
Page
(Sub-header
and
Element
Descriptor)
The
Element
Status
Page
includes
an
8-byte
sub-header
and
one
or
more
element
descriptors.
The
sub-header
includes
the
element
type
code,
the
settings
for
PVolTag
and
AVolTag,
the
length
of
each
descriptor
block,
and
the
number
of
bytes
of
descriptor
information
that
follow
the
header
for
the
element.
Bit
7
6
5
4
3
2
1
0
Byte
0
Element
Type
Code
1
PvolTag
AvolTag
Reserved
2
-
3
Element
Descriptor
Length
3-54
TL2000
and
TL4000
SCSI
Reference