SCSI Vendor Unique Command Latency Measurement in Storage Area Networks
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Solution Overview
Problem
Existing methods for measuring latency or round-trip time in storage area networks (SANs) are unreliable due to queueing delays, which skew measurement results and impact application performance, especially in environments with multiple hosts and busy storage arrays.
Innovation Solution
A method and system that utilize a SCSI Vendor Unique (VU) command to measure latency by ensuring the command is not enqueued for later handling, allowing for a direct and immediate response, thereby minimizing processing delay and providing an accurate round-trip time measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard SCSI commands are used for latency measurement, then the measurement process is compatible with existing storage protocols, but queueing delays occur that skew measurement results
Solution Approach 1:
The patent changes the command type parameter from standard SCSI commands to SCSI Vendor Unique (VU) commands. This parameter change ensures that the storage array processes these specific VU commands immediately without enqueuing them, thereby eliminating queueing delays while maintaining compatibility with existing SCSI protocol infrastructure. The measurement accuracy is improved by selecting a command type that bypasses the normal queuing mechanism.
2Productivity
If multiple hosts access the storage array simultaneously, then resource sharing and productivity are improved, but measurement reliability deteriorates due to increased queueing delays
Solution Approach 1:
The patent extracts the measurement operation from the normal command processing queue by using a special VU command type. This separation allows latency measurements to be performed independently of the queueing dynamics caused by multiple hosts accessing the storage array. The measurement process is thus isolated from the productivity-enhancing multi-host operations, ensuring measurement reliability is not compromised by resource sharing activities.
3Reliability
If commands are evaluated and processed by the storage array, then functional operation is maintained, but processing delays are introduced that affect measurement precision
Solution Approach 1:
The patent implements preliminary action by designing the VU command to be recognized and processed immediately upon receipt, before it can be enqueued for later handling. The storage array is pre-configured to identify VU commands and execute them with minimal delay, ensuring that the functional evaluation requirement is met while the processing delay is reduced to a negligible level for measurement purposes.
Data Source
AI summary
A method, system, and computer program product for measuring latency in storage area networks comprising receiving a command from a node at a first time by a target in a storage area network, evaluating the command by the target, and returning a reply to the node from the target at a second time, wherein a difference between the second time and the first time is less than a time period indicative of a processing delay in the target, wherein the reply is considered a good status reply.