RE: [t13] WRITE LONG, SCT Write Long, and WRITE WRONG EXT

[Sheffield, Robert L]

Along the thread of being helpful to SCSI-to-ATA Translation (SAT): There's a related capability I think should be addressed ahead of the Read/Write Long capabilities.

 

The SCSI SBC-2 standard defines the TB bit in the Read/Write error recovery mode page as follows:

A transfer block (TB) bit set to zero specifies that the device server shall not transfer a logical block to the

data-in buffer if the logical block is not recovered within the recovery limits specified. A TB bit set to one

specifies that the device server shall transfer a logical block to the data-in buffer before returning CHECK

CONDITION status if the logical block is not recovered within the recovery limits specified. The data returned

in this case is vendor-specific. The TB bit does not affect the action taken for recovered data.

The net effect is the ability of a SCSI disk drive to transfer a block of data read from the media, even though there were uncorrectable/unrecoverable errors. Presumably (though not specified) the disk would return data that matches the orignially written data except for the bits/bytes affected by the media defect. Without a comparable feature in the ATA command set, the only way SAT device can SATisfy (sorry) the required behavior for a TB set to one is to manufacture the data - which doesn't really meet the spirit of what the TB feature was intended to accomplish.

 

Perhaps this could be done with some form of read/write long (or wrong), but the problem with those commands is the ECC algorithm applied is vendor-specific, and the host application needs to comprehend the vendor-specific aspects of the device ECC algorithm in order to reliably "plant" bad ECC that can be distinguished from an actual bad block. I'd like to see a standard ATA command that allows retrieval of whatever good information can be extracted from a bad block that isn't dependent on vendor-specific aspects of the ECC algorithm applied (i.e. doesn't transfer the ECC bytes).

 

Bob

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From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Elliott, Robert (Server Storage)
Sent: Wednesday, June 08, 2005 5:11 PM
To: forum@t13.org
Subject: [t13] WRITE LONG, SCT Write Long, and WRITE WRONG EXT

ATA offers quite a few ways to perform WRITE LONG and READ LONG functionality.

 

1. ATA-3 defined WRITE LONG (command codes 32h and 33h) and READ LONG

(command codes 22h and 23h), including a note that "The committe is considering removing READ LONG and WRITE LONG commands in a future ATA standard." The commands are obsolete in ATA-4.

 

2. The SCT (SMART Command Transport) technical report defines a way to implement WRITE LONG and READ LONG commands through SMART log pages (supporting 48-bit LBAs).

 

Command: SMART READ LOG, SMART WRITE LOG, READ LOG EXT, or WRITE LOG EXT

Log address: E0h (Writes) or E1h (Reads)

SCT Function code: 0001h (Read Long) and 0002h (Write Long)

 

Those log addresses are marked "Reserved" in ata7v1r4b.

 

3. Proposal e02126, defining new WRITE WRONG EXT and READ WRONG EXT commands, has apparently been resurrected.

 

 

Any chance of converging on one method?  If WRITE WRONG continues, then a SCSI equivalent would be helpful for the SCSI-to-ATA Translation (SAT) project.

 

Since these commands each address a single logical block, it's unclear how well they will work with long physical sectors, where the ECC bytes are shared by more than one logical block.

 

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Rob Elliott, [EMAIL PROTECTED]
Hewlett-Packard Industry Standard Server Storage Advanced Technology
https://ecardfile.com/id/RobElliott