Acer SmartRAID V Bedienungsanleitung PDF herunterladen (Seite 191)

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Theory of Operation

Command Processing

The I

O messaging protocol is based on the existence of a messaging

FIFO (first-in, first-out) queue and a reply FIFO queue. Each queue

consists of a list of message frames. The messaging queue contains

requests for I/O processing that are read by the HDM. The reply queue is

where completion statuses are posted by the controller and read by the

OSM. DPT SmartRAID V controllers use I

O messaging to process a

command from the host computer as follows:

1. The OSM acquires a frame in controller RAM from the messaging

queue on the controller, fills it out and returns it to the messaging

queue to initiate the I/O command.

2. The controller HDM firmware processes the frame.

3. The controller completes the I/O command; transferring data if

necessary.

4. The controller acquires a frame from the reply queue, fills it out and

returns it to the queue and issues an interrupt.

5. On interrupt, the OSM retrieves the completed reply frame from

the reply queue and uses the information in the frame to complete

the I/O operation. It then returns the frame to the reply queue.

Command Overlapping

Command overlapping is a technique that lets a controller receive and

respond to multiple host requests before any particular request is

completed. SmartRAID V controllers can receive additional commands

before the previous command has finished executing. By allowing multiple

outstanding commands, SmartRAID V controllers can optimize

performance by overlapping commands for multiple devices, thereby

keeping all devices busy as much as possible. The Decade and Century

family of controllers can queue up to 2000 commands. The Millennium

family of controllers can queue up to 8000 commands.

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Acer SmartRAID V Bedienungsanleitung Seite 191