Seagate ST1000VX000 SV35 Series PATA Product Manual - Page 46
Urgent bit, Flush to Disk bit, Not Sequential bit, Read Continuous bit, Write Continuous bit, Handle
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The streaming commands may access any user LBA on a device. These commands may be interspersed with non-streaming commands, but there may be an impact on performance due to the unknown time required to complete the non-streaming commands. The streaming commands should be issued using a specified minimum number of sectors transferred per command, as specified in word 95 of the IDENTIFY DEVICE response. The transfer length of a request should be a multiple of the minimum number of sectors per transfer, as should the starting LBA of any streaming command. Urgent bit The Urgent bit in the READ STREAM and WRITE STREAM commands is ignored. Therefore, bits 9 and 10 of IDENTIFY DEVICE data words 84 and 87 shall remain clear. Flush to Disk bit The Flush to Disk bit in the WRITE STREAM command specifies that all data for the specified stream shall be flushed to the media before posting command completion. If a host requests flushes at times other than the end of each Allocation Unit, streaming performance may be degraded. Using the SET FEATURES command to enable/disable caching may not affect caching for streaming commands. Not Sequential bit The Not Sequential bit specifies that the next LBA(s) after those requested in the current READ STREAM command are not anticipated to be used in a subsequent READ STREAM command. This information may help the device with pre-fetching decisions. Read Continuous bit If the Read Continuous bit is set to 1 for the command, the device shall attempt to transfer the requested amount of data to the host within the Command Completion Time Limit even if an error occurs. The data sent to the host by the device in an error condition is vendor specific. Write Continuous bit If the Write Continuous bit is set to 1 for the command and an error is encountered, the device shall still attempt to complete the transfer within the requested time. If an error occurs and cannot be resolved within the Command Completion Time Limit, the erroneous section on the media may be unchanged or may contain undefined data. A future read of this area may not report an error, even though the data is erroneous. If the Flush Bit is set to 1 on the STREAM WRITE command and the data cannot successfully be written to the media, then the drive will report a Stream Error on the command. Handle Streaming Error bit The Handle Streaming Error bit specifies to the drive that this command starts at the LBA of a recently reported error section, so the device may attempt to continue its corresponding error recovery sequence where it left off earlier. This mechanism allows the host to schedule error recovery and defect management for content critical data. 40 SV35 Series Product Manual, Rev. B