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Method for Timing SCSI Commands based upon expected Command Execution Time

IP.com Disclosure Number: IPCOM000103783D
Original Publication Date: 2005-Mar-18
Included in the Prior Art Database: 2005-Mar-18
Document File: 1 page(s) / 31K

Publishing Venue

IBM

Abstract

Small computer system interface (SCSI) Device Drivers assign command time-out values are based upon the command type such as Read, Write, Format, etc. This invention proposes that for media access commands such as Read or Write SCSI Commands that the time-out value be based upon the amount of data being requested.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 74% of the total text.

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Method for Timing SCSI Commands based upon expected Command Execution Time

Disclosed is a method for varying the Command time-out value used by SCSI Device Drivers based upon the amount of data to be transferred. Typically SCSI Device Drivers assign fixed Command Time-out values for SCSI commands to complete based upon the type of command such as Read, Write, Format, etc. When a storage device is having to perform error recovery procedures the time it takes to complete media access commands such as reads or writes can vary significantly. The actual time it takes the storage device to complete the command is directly proportional to the number of blocks of data being requested in the SCSI Command Descriptor Block (CDB). Thus a SCSI read or write command that only requests a single block or 8 blocks (4096 bytes) of data normally takes considerably less time to complete than a command transferring 256 blocks of data. Since it is desirable to set the command time-out values to as small as possible values for system performance reasons storage devices end up having commands requesting large block transfers aborted because insufficient time is given for them to complete. If the SCSI command time-out value were set based upon the block length giving less time for small data requests and more time to commands requesting more data overall system throughput could be improved. This is because the typical error recovery for a command time-out is to issue an SCSI Abort or Res...