SCSI CDB: logical block address & transfer length

Mcgrath, Jim Jim_Mcgrath at maxtor.com
Tue Mar 5 17:48:24 PST 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Mcgrath, Jim" <Jim_Mcgrath at maxtor.com>
*
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The LBA is always the first block requested for the command.  The
transfer length is actually in blocks, and it tells you how many
additional sequential blocks to transfer.  i.e. an LBA of 10 and
transfer length of 3 indicates to transfer LBAs 10, 11, and 12.  In
general there is no ability to transfer non contiguous blocks in a
single command.
 
Jim
 

-----Original Message-----
From: Lin Zhu [mailto:lzhu at powersurfr.com]
Sent: Tuesday, March 05, 2002 5:00 PM
To: t10 at t10.org
Subject: SCSI CDB: logical block address & transfer length
Importance: High


Hi All,
 
I'm a little confused about the relationship between "logical block
address" and "transfer length" specified in CDB format. The logical
block address in CDB tells the target where the information is located
on the physical medium, while the transfer length tells the target how
much data to transfer, usually as an amount of blocks. 
 
My question is: suppose the transfer length(say, 128KB) is larger than a
block size(8KB) then how to specify the value of logical block
address(es) since the data will spread across multiple blocks (in this
example, 16 blocks) ?  Can someone please help me with this problem?
Thanks so much in advance.
 
Lin


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 The LBA is always the first block requested for the command.  The transfer length is actually in blocks, and it tells you how many additional sequential blocks to transfer.  i.e. an LBA of 10 and transfer length of 3 indicates to transfer LBAs 10, 11, and 12.  In general there is no ability to transfer non contiguous blocks in a single command.
  
 Jim
  
 -----Original Message-----
From: Lin Zhu [mailto:lzhu at powersurfr.com]
Sent: Tuesday, March 05, 2002 5:00 PM
To: t10 at t10.org
Subject: SCSI CDB: logical block address & transfer length
Importance: High


 Hi All,
  
 I'm a little confused about the relationship between "logical block address" and "transfer length" specified in CDB format. The logical block address in CDB tells the target where the information is located on the physical medium, while the transfer length tells the target how much data to transfer, usually as an amount of blocks. 
 
 My question is: suppose the transfer length(say, 128KB) is larger than a block size(8KB) then how to specify the value of logical block address(es) since the data will spread across multiple blocks (in this example, 16 blocks) ?  Can someone please help me with this problem? Thanks so much in advance.
  
 Lin


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