Streaming Feature Set - Hitachi CinemaStar P7K500 Specifications

8.16 Streaming feature Set

The Streaming feature set is an optional feature set that allows a host to request delivery of data from a
contiguous logical block address range within an allotted time. This places a priority on time to access the
data rather than the integrity of the data. Streaming feature set commands only support 48-bit addressing.
A device that implements the Streaming feature set shall implement the following minimum set of
commands:
Configure Stream
Read Stream PIO
Write Stream PIO
Read Stream DMA
Write Stream DMA
Read Log Ext
Support of the Streaming feature set is indicated in Identify Device work 84 bit 4.
Note that PIO versions of these commands limit the transfer rate (16.6 MB/s), provide no CRC protection,
and limit status reporting as compared to a DMA implementation.
8.16.1 Streaming commands
The streaming commands are defined to be time critical data transfers rather than the standard data integrity
critical commands. Each command shall be completed within the time specified in the Configure Stream
command or in the streaming command itself in order to ensure the stream requirements of the AV type
application. The device may execute background tasks as long as the Read Stream and Write Stream
command execution time limits are still met.
Using the Configure Stream command, the host may define the various stream properties including the
default Command Completion Time Limit (CCTL) to assist the device in setting up its caching for best
performance. If the host does not use a Configure Stream command, the device shall use the CCTL
specified in each streaming command, and the time limit is effective for one time only. If the CCTL is not set
by Configure Stream command, the operation of a streaming command with a zero CCTL is device vendor
specific. If Stream ID is not set by a Configure Stream command, the device shall operate according to the
Stream ID set by the streaming command. The operation is device vendor specific.
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.
The host provided numeric stream identifier, Stream ID, may be used by the device to configure its
resources to support the streaming requirements of the AV content. One Stream ID may be configured for
each read and write operation with different command completion time limits be each Configure Stream
command.
8.16.1.1
Urgent bit
The Urgent bit in the Read Stream and Write Stream commands specifies that the command should be
completed in the minimum possible time by the device and shall be completed within the specified
Command Completion Time Limit.
8.16.1.2
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. The Set Features command to
enable/disable caching shall not affect caching for streaming commands.
8.16.1.3
Not Sequential bit
HITACHI Deskstar & CinemaStar P7K500 Hard Disk Drive specification (Rev 1.1)
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