Extended Copy: Ambiguities regarding inexact segments and CAT bit

chamb at almaden.ibm.com chamb at almaden.ibm.com
Tue Jan 4 13:04:40 PST 2000


* From the T10 Reflector (t10 at t10.org), posted by:
* chamb at almaden.ibm.com
*


Is anyone working on revisions to the section of SPC-2 containing
specifications for the Extended Copy command?  I have been designing
application code to exploit Extended Copy and have found places where the
specifications appear to be incomplete.

In T10/1236-D rev 14 the specifications for Extended Copy do not define the
results for some situations with CAT=1 and inexact segments.  Specifically:

1.  If CAT=1 on an inexact segment, "the remainder of the destination block
data shall be taken from the next segment."  What does the standard require
of the target if the next segment has a different destination?

2.  If CAT=1 and the data read from the source exceeds the length specified
by the segment, what does the standard require the target to do with the
remaining source data?  This can occur for Stream-to-Discard,
Stream-to-Block, or Stream-to-Stream (with DC=1).  If the data is held for
future segments, what does the standard require the target to do if the
next segment specifies a different source, or specifies inline or embedded
data?

3. What results are specified in the standard for the parameter set
described below:
Contents are described in terms of labeled 256-byte chunks, e.g. A00.
Target 0 is a source tape A with 2048-byte blocks
   block 0 = [A00 A01 A02 A03 A04 A05 A06 A07]
   block 1 = [A10 A11 A12 A13 A14 A15 A16 A17]
Target 1 is a source tape B with 2048-byte blocks
   block 0 = [B00 B01 B02 B03 B04 B05 B06 B07]
   block 1 = [B10 B11 B12 B13 B14 B15 B16 B17]
Target 2 is a destination tape C to which 512-byte blocks will be written

Segment 0  code 06h (Str-to-discard) CAT=1  Src=0  XferLen=2048 Bytes=256
Segment 1  code 03h (Str-to-str) CAT=1 DC=1  Src=0  Dest=2
                     SrcXferLen=2048 DestXferLen=512 Count=1
Segment 2  code 06h (Str-to-discard) CAT=1  Src=0  XferLen=2048 Bytes=256
Segment 3  code 03h (Str-to-str) CAT=1 DC=1  Src=0  Dest=2
                     SrcXferLen=2048 DestXferLen=512 Count=1
Segment 4  code 06h (Str-to-discard) CAT=1  Src=1  XferLen=2048 Bytes=256
Segment 5  code 03h (Str-to-str) CAT=0 DC=1  Src=1  Dest=2
                     SrcXferLen=2048 DestXferLen=512 Count=1

Conceivable results could include:
   Error?  C contents                   Next block for A  for B
a. No     [A01 A02] [A04 A05] [B01 B02]                1      1
b. No     [A01 A02] [A04 A05] [A07 B00]                1      1
c. No     [A01 A02] [A11 A12] [B01 B02]                2      1
d. No     [A10 A11] [A30 A31] [B10 B11]                4      2
e. Yes    [A01 A02] [A04 A05]                          1      0


David Chambliss
Research Staff Member, Computer Science /Storage Systems
IBM Research Division
(408) 927-2243  (TL 457-2243)
FAX (408) 927-3497


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