[t13] 04-136r0.pdf SCSI to ATA Command Translations

[James.C.Hatfield at seagate.com]

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Fixing the bytes/LBA at 512 is not acceptable.

In ATA/ATAPI-7, T13 established support for
      * long LBAs
      * multiple LBAs/physical sector
      * multiple physical sectors/LBA

Thank You !!!
-----------------------------------------------------------------
Jim Hatfield
ATA Interface Firmware & T13 (ATA/ATAPI) Standards Representative
Seagate Technology - PSG
   e-mail:  James.C.Hatfield at seagate.com
   s-mail:  389 Disc Drive;  Longmont, CO 80503 USA
   voice:   720-684-2120
   fax    :    720-684-2711
====================================================


|---------+---------------------------->
|         |           Jeff Garzik      |
|         |           <jgarzik at pobox.co|
|         |           m>               |
|         |           Sent by:         |
|         |           owner-forum at t13.o|
|         |           rg               |
|         |           No Phone Info    |
|         |           Available        |
|         |                            |
|         |           06/07/2004 09:24 |
|         |           AM               |
|         |                            |
|---------+---------------------------->
  >--------------------------------------------------------------------------------------------------------------|
  |                                                                                                              |
  |       To:       Joerg Schilling <schilling at fokus.fraunhofer.de>                                              |
  |       cc:       p.lavarre at ieee.org, forum at t13.org, t10 at t10.org                                               |
  |       Subject:  Re: [t13] 04-136r0.pdf SCSI to ATA Command Translations                                      |
  >--------------------------------------------------------------------------------------------------------------|




This message is from the T13 list server.


Joerg Schilling wrote:
>>From owner-t10 at t10.org  Fri Jun  4 21:14:23 2004
>
>
>>>>3.2 Read Capacity (10) Command  (25h)
>>>>() BLOCK LENGTH IN BYTES
>>>>This value is currently set to 512 bytes,
>>>>which is the standard sector size for disk drives.
>>>
>>>
>>>I see us taking the chance to try to fix the bytes/LBA at 0.5 Ki, like
>>>MMC fixed the bytes/LBA at 2 Ki, shutting out the (empty set of?) ATA MO
>>>folk.
>>>
>>>I like that.
>
>
>>It shut out nobody.
>
>
>>IMO the OS request block size _should_ be constant at 512 octets.  It
>>makes calculations easier, and representations more normal.
>
>
> Please do not forget CD/DVD writers.
>
> They use 2048 Bytes per block.

That's fine, it's a multiple of 512.

It's rather nice when the kernel block or filesystem driver can simply
store a shift count, and then do

BASE_SECTOR_SHIFT=9
dvd_wr_sector_shift=2
device_sector_shift=BASE_SECTOR_SHIFT + dvd_wr_sector_shift
block_bytes = (1 << device_sector_shift)

Storing things as a power-of-2 is very efficient on a number of host
platforms.  And basing things off of a fixed base -- 9 (512 bytes) --
makes life even easier.

             Jeff