Access Control Apparatus Path Switching Mechanism
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Solution Overview
Problem
Multipath storage systems face challenges in reducing response time to access requests while minimizing data destruction, especially when the operating system does not support cancel commands and path failures occur.
Innovation Solution
An access control apparatus that outputs an access command through a first path and, upon no response within a predetermined time, controls a second controller to stop processing by the first controller and switches to the second path, allowing for immediate output of the access command without waiting for an error response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system waits for an error response from the first path before switching to the second path, then data destruction is minimized, but the response time to access requests increases
Solution Approach 1:
The invention sends a preliminary stop processing command to the first controller through the second path before the first path times out. This preliminary action prevents the first controller from continuing to process the I/O request after the path failure, thereby preventing data destruction while allowing the system to switch to the second path without waiting for the timeout period to elapse.
2Loss of time
If the system switches to the second path immediately without waiting for error response, then access response time is reduced, but data destruction risk increases
Solution Approach 1:
The invention applies preliminary anti-action by sending a stop processing command to the first controller before the actual path failure takes effect. This counteracts the potential harmful effect of data destruction that would occur if the system immediately switched paths without preventing the first controller from continuing its processing.
3Ease of operation
If the OS supports cancel commands, then path switching is simpler, but compatibility with systems without cancel command support is reduced
Solution Approach 1:
The invention introduces an intermediary mechanism by using a second controller as a mediator to send stop processing commands to the first controller. This intermediary approach allows the system to achieve path switching functionality similar to cancel commands without requiring direct OS support for cancel commands, thereby maintaining compatibility with various operating systems.
Data Source
AI summary
An access control apparatus includes a memory, and a processor coupled to the memory and configured to, in response to an access request to a storage device, output an access command through a first path to a first controller among a plurality of controllers that control the storage device, the access command being a command to access the storage device, when no response to the access command to the first controller is received before a predetermined time passes after the output of the access command, control a second controller different from the first controller among the plurality of controllers through a second path coupled to the second controller such that the second controller stops processing executed by the first controller according to the access command, and output the access command through the second path after receiving a response to the control on the second controller.