IBM DARA-206000 Hard Drive Specifications - Page 105

Delayed Write Function Vendor Specific

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10.12 Delayed Write Function (Vendor Specific) Delayed Write function is a power saving enhancement whereby the device delays the actual data writing into the media. When the device is in the power saving mode and the Write command (Write Sectors, Write Multiple, or Write DMA) comes from the host, the transferred data is not written into the media immediately, only stored into the cache buffer. When the cache buffer becomes full or reaches to the predefined size, or any command except the Write command comes, the operation to write the data in the cache buffer into the media is started. Here is reason why the power consumption can be reduced by Delayed Write. When some Write commands comes with enough long interval, the device must exit from the power saving mode and enter into the power saving mode again without Delayed Write function. If Delayed Write is enabled, such power saving mode transition times can be reduced. As result, the additional energy for power saving mode transition can be saved, then the average power consumption of the device can be reduced. But the duration since the command completion of the Write command until the media write completion will be extended terribly with Delayed Write function. If the power for the device is turned off in this duration, the data which has not been written to the media is lost. So a command listed in Write Cache Function section shall be issued before the power off to confirm whole cached data has been written into the media. For safety, Delayed Write function is disabled at Power On Default. Enable Delayed Write command shall be issued to the device to enable Delayed Write function every Power On Reset or Hard Reset. The actions of each reset is shown in Figure 57 on page 74 10.12.1 Enable/Disable Delayed Write command Command code FAh with Feature register 07h enables Delayed Write function. Command code FAh with Feature register 87h disables Delayed Write function. Be careful that even if Delayed Write function is enabled by this command, Delayed Write does not work when Write Cache function is disabled. General Operation Descriptions 95

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10.12
Delayed Write Function (Vendor Specific)
Delayed Write function is a power saving enhancement whereby the device delays the actual data writing
into the media. When the device is in the power saving mode and the Write command (Write Sectors, Write
Multiple, or Write DMA) comes from the host, the transferred data is not written into the media imme-
diately, only stored into the cache buffer.
When the cache buffer becomes full or reaches to the predefined
size, or any command except the Write command comes, the operation to write the data in the cache buffer
into the media is started.
Here is reason why the power consumption can be reduced by Delayed Write.
When some Write com-
mands comes with enough long interval, the device must exit from the power saving mode and enter into the
power saving mode again without Delayed Write function. If Delayed Write is enabled, such power saving
mode transition times can be reduced. As result, the additional energy for power saving mode transition can
be saved, then the average power consumption of the device can be reduced.
But the duration since the command completion of the Write command until the media write completion
will be extended terribly with Delayed Write function.
If the power for the device is turned off in this dura-
tion, the data which has not been written to the media is lost.
So a command listed in Write Cache Func-
tion section shall be issued before the power off to confirm whole cached data has been written into the
media.
For safety, Delayed Write function is disabled at Power On Default.
Enable Delayed Write command shall
be issued to the device to enable Delayed Write function every Power On Reset or Hard Reset.
The actions
of each reset is shown in Figure 57 on page 74
10.12.1
Enable/Disable Delayed Write command
Command code FAh with Feature register 07h enables Delayed Write function.
Command code FAh with Feature register 87h disables Delayed Write function.
Be careful that even if Delayed Write function is enabled by this command, Delayed Write does not work
when Write Cache function is disabled.
General Operation Descriptions
95