pCRC interval for Duoble Transition, non-IU transfers

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Tue Aug 12 06:35:12 PDT 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*

Most implementations use the logical block size, often 512 bytes. I suppose
tapes would use their record size. I wouldn't go more than 4K bytes in a
data group if you choose to merge multiple blocks into a single data group.



                                                                                                                  
                      "Mark Emmer"                                                                                
                      <marke at snobol4.co        To:       <t10 at t10.org>                                            
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                      Sent by:                 Subject:  pCRC interval for Duoble Transition, non-IU transfers    
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* From the T10 Reflector (t10 at t10.org), posted by:
* "Mark Emmer" <marke at SNOBOL4.com>
*
Hello all,

I'm looking for guidance on selecting pCRC intervals (i.e., Data Group
lengths)
for non-packetized, wide, Fast-10 through Fast-80 Double Transition data
transfers.  (IU=0, DT=1 in PPR message).

Searching SPI-4, there does not appear to be any mode page setting that
controls
this value, which I guess makes sense since the interval is completely
under the
control of the target for both DT Data In and DT Data Out.

Given the dilution of pCRC strength with increasing Data Group length, one
would
not want to be doing a megabyte transfer and relying solely on a single,
end-of-transfer pCRC for data integrity.

Are there any commonly accepted values (2 KB, 4 KB, etc.) for partitioning
a
long transfer into smaller data groups?

Thank you,

Mark Emmer



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