Proposal for SSC

Hallam, Ken MV KHallam at po2.mv.unisys.com
Fri Apr 12 08:17:00 PDT 1996


* From the SCSI Reflector, posted by:
* "Hallam, Ken                 MV" <KHallam at po2.mv.unisys.com>
*

SCSI Reflectorites,

Here is a proposal for consideration by the SSC working group.

Accredited Standards Committee

X3, Information Processing Systems
                                                Doc:    X3T10/96-155R0
                                                Date:   April 11, 1996
                                                Project:X3T10/997-D
                                                Ref. Doc.: 997R06
                                                Reply to: Ken Hallam
                                                Unisys
                                                ken.hallam at mv.unisys.com



To:      X3T10 SSC Working Group Membership
Subject: Proposal for SSC Log Page 0Ch


Problem:
The SSC draft provides a way for tape drives to inform the host that
cleaning is required by means of Log Page code 0Ch, (Sequential-access
Device Log Page) and Log Parameter code of  0100h. A non zero value in
the Log Parameter returned under this code indicates that the drive
requires cleaning. However, there is no guidance in the draft regarding
the length of the parameter. Some existing models of tape products in
the field today use parameter code 0100h with a parameter length of 8
bytes, while others use a parameter length of 2 bytes. A variable length
for this parameter value is a problem. Parsing a multiple byte field to
check for non-zero content is not efficient. In addition, it is
difficult to pre-allocate space for a variable field in software that
must deal with many different models of tape drives.

Proposal:
Modify the paragraph following Table 26 in clause 5.3.2.1 of draft 997
by adding the following text to the end of the paragraph:

"The parameter value returned under parameter code 0100h shall be a 2
byte field, thus byte 3 of the Log Parameter header shall be set to
02h."


              Table 26
Parameter Code     Description
0000h              Number of data bytes received from application
                   clients during WRITE command operations.
0001h              Number of data bytes written to the media as a
                   result of WRITE command operations, not counting ECC
                   and formatting overhead.
0002h              Number of data bytes read from the media during READ
                   command operations, not counting ECC and formatting
                   overhead.
0003h              Number of data bytes transferred to Data-Out buffers
                   during READ command operations.
0004h - 00FFh      Reserved
0100h              Cleaning required
0101h - 7FFFh      Reserved
8000h - FFFFh      Vendor-specific parameters

A non-zero value of the cleaning required parameter indicates that a
condition requiring cleaning has been detected and a subsequent cleaning
cycle has not been completed. The cleaning required parameter shall be
persistent across hard resets and power cycles. "The parameter value
returned under parameter code 0100h shall be a 2 byte field, thus byte 3
of the Log Parameter header shall be set to 02h."


Regards,

Ken Hallam
Unisys
ken.hallam at mv.unisys.com




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