3 XCOPY problems

Steve Wilson steve at crossroads.com
Thu May 20 09:23:39 PDT 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* Steve Wilson <steve at Crossroads.com>
*

Joseph,

As far as the pad usage is concerned, the behavior described in Table 23,
src pad=1, dst pad=0, cat =0 , when a transfer is enacted, specifies that
the src pad bit defines source "stripping" when the source transfer length
for the segment is larger than the destination transfer length. Even though
the source transfer length is a multiple of the source block size, I
understand the source padding bit to have another use, which is the
stripping of data that cannot be transfered to the destination block(s).
Therefore, in this case I would not consider the src pad bit to be a no-op.

One could make an argument as to whether the behavior I described is useful.

steve

Steve Wilson steve at crossroads.com
T 512.794.2716	  F 512.349.0304
"Routing Infinibytes" 
Crossroads Systems    Austin, Texas



-----Original Message-----
From: Joseph C. Nemeth [mailto:jnemeth at concentric.net]
Sent: Wednesday, May 19, 1999 12:14 PM
To: roweber at acm.org
Cc: t10 at Symbios.COM
Subject: Re: 3 XCOPY problems

[stuff deleted]

Pad problem:

For me, there is a conceptual problem with "source padding" on copy
operations where the source controls the transfer count, and "destination
padding" on copy operations where the destination controls the transfer
count. If the source determines the transfer count, it will always be a
multiple of the source block size, and so "source padding" should be a
no-op. However, if neither 'cat' nor 'dst pad' are set, there are cases
where you can't flush the data, and it seems to me that in these cases, the
'src' bit should be ignored, and this should be treated as a "no-cat,
no-src-pad, no-dst-pad" condition and cause a copy error with UNEXPECTED
INEXACT SEGMENT, even though the 'src pad' bit is set. Ditto for the 'dst
pad' bit when the destination controls the transfer count.

I think the standard should clarify this, as well.


Joseph C. Nemeth          Precision Algorithms          (970) 226-5427
contact:                         Spectra Logic                    (303)
449-6400x1102

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