Echo mode, Echo buffer descriptor mode, Echo – Dell PowerVault TL2000 User Manual
Page 66: Mode, Buffer, Descriptor
Bit
7
6
5
4
3
2
1
0
Byte
0
-
n
(data
defined
by
previous
Data
Mode
WRITE
BUFFER
command)
Echo
Mode
In
this
mode,
the
library
returns
the
same
number
of
bytes
of
data
as
received
in
the
prior
Echo
Mode
WRITE
BUFFER
command
from
the
same
host.
If
a
prior
Echo
Mode
WRITE
BUFFER
command
did
not
complete
successfully
the
Echo
Mode
READ
BUFFER
command
shall
return
Check
Condition
status.
The
sense
key
shall
be
set
to
ILLEGAL
REQUEST
and
the
sense
data
shall
be
set
to
COMMAND
SEQUENCE
ERROR.
If
the
data
in
the
Echo
Buffer
has
been
overwritten
by
another
host
the
library
shall
return
Check
Condition
status.
The
sense
key
shall
be
set
to
ILLEGAL
REQUEST
and
the
sense
data
shall
be
set
to
ECHO
BUFFER
OVERWRITTEN.
The
maximum
length
of
the
Echo
Mode
buffer
is
256
bytes.
Bit
7
6
5
4
3
2
1
0
Byte
0
-
n
(data
defined
by
previous
Echo
Mode
WRITE
BUFFER
command)
Echo
Buffer
Descriptor
Mode
In
this
mode,
the
media
changer
returns
the
descriptor
information
for
the
Echo
Buffer.
The
Buffer
Offset
field
is
reserved
in
this
mode.
The
Buffer
ID
field
is
ignored
in
this
mode.
Next
table
specifies
the
Buffer
Descriptor
which
is
returned
on
a
READ
BUFFER
command
in
Echo
Buffer
Descriptor
Mode.
Bit
7
6
5
4
3
2
1
0
Byte
0
Reserved
EBOS
1
Reserved
2
Reserved
(MSB)
3
Buffer
Capacity
(LSB)
Field
descriptions:
EBOS:
The
Echo
Buffer
Overwritten
Support
bit
is
set.
The
library
shall
return
ECHO_BUFFER_OVERWRITEN
sense
data
when
the
buffer
is
overwritten
by
another
initiator.
Buffer
Capacity:
The
Buffer
Capacity
field
returns
the
maximum
size
of
the
Echo
Buffer
in
bytes.
The
Echo
Buffer
can
store
up
to
256
bytes.
3-52
TL2000
and
TL4000
SCSI
Reference