Hard Drives White Papers
A Command Queuing Engine Raises Bar for Increased Hard Drive Performance
Overview When accessing sequentially stored data, the highest sustainable transfer rate between a host controller and a hard drive is the disk transfer rate. If the transfer length of individual commands is small, the firmware overhead associated with each command causes an adverse affect on the transfer rate. Command queuing allows some portion of the overhead to occur parallel to other operations, but does not sufficiently reduce the overhead to obtain the desired disk transfer rate. To achieve higher sequential transfer rates, a reduction or elimination of the firmware overhead is necessary. In current SCSI ASICs, there is very little, if any, automation provided to allow multiple, related commands to be received and completed without the intervention of the firmware. This is especially true in a command queuing environment where multiple commands are received before the first command can be started. This can result in poor sequential performance since the firmware overhead, which is required to set up the data transfer, occurs between commands and directly contributes to performance degradation. The Command Queuing Engine, or CQE, was invented in order to alleviate the overhead between the completion of one command and the execution of the next in a command queuing environment.
| Publisher | Western Digital Corporation | File Format | HTML & PDF |
|---|---|---|---|
| Date Published | October 1998 | Downloads | 13 |
| Format | White Papers | ||
| Topics | |||
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