Virtual SAS Expander for Tape Library Path Redundancy
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Solution Overview
Problem
In SAS systems, when a media changer or data transfer device fails, the communication link is lost, disrupting the operation of other drives in a tape library, as existing technologies do not efficiently manage multi-path connections to maintain functionality across different physical paths.
Innovation Solution
A virtual SAS expander is created by embedding a SAS protocol chip within a target device, allowing it to emulate expander functions and switch configurations to maintain media changer exposure through different data transfer devices, presenting multiple unique target devices to the initiator without requiring special software on the initiator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a media changer uses a SAS interface hosted by a data transfer device to present logical units to an initiator, then the connection method is simplified, but if the data transfer device fails, the communication link is lost and all drives in the library become unusable
Solution Approach 1:
The patent segments the media changer connection by creating separate SAS connections from the initiator to multiple data transfer devices, each independently connected to the media changer. This segmentation ensures that a failure in one data transfer device does not affect other drives, as each has its own independent communication path to the media changer.
Solution Approach 2:
The patent introduces additional data transfer devices as intermediaries between the initiator and the media changer. These intermediaries provide alternative communication paths, so that if one intermediary fails, the initiator can still communicate with the media changer through other intermediaries, maintaining system reliability.
2Reliability
If multi-pathing is implemented to present the same storage device through two different paths using two different names, then path redundancy is achieved, but special software application is required between application and host bus adapters to convert paths into single logical path
Solution Approach 1:
The patent enables the SAS initiators to automatically discover and manage multiple paths to the media changer through standard SAS protocols without requiring special software applications. The initiators self-configured to recognize multiple data transfer devices and their connections to the media changer, eliminating the need for external path conversion software.
Solution Approach 2:
The patent makes standard SAS initiators universal by enabling them to natively handle multiple paths to the same media changer through conventional SAS protocol extensions. This multi-functionality allows any standard initiator to manage path redundancy without requiring specialized software, as the capability is built into the initiator itself.
3Adaptability or versatility
If the same storage device is presented through two different paths using two different names called multi-pathing, then communication redundancy is achieved, but the system requires special software application installed between application and host bus adapters
Solution Approach 1:
The system performs self-service by having SAS initiators automatically discover and manage multiple paths to storage devices through standard SAS protocols. The initiators self-configure to recognize alternative paths without requiring manual software installation, making the system easier to deploy and maintain while maintaining communication redundancy.
Data Source
AI summary
A method, system and computer readable medium for presenting unique Serial Attached Small computer system interface (SAS) target devices through a single target device. The method includes embedding a SAS protocol chip within an initiator-connectable device, the SAS protocol chip having storage for at least two SAS addresses and configured to select a single address, loading two or more SAS addresses into the SAS protocol chip, and mapping a respective SAS address to one of the unique target devices. The system includes a SAS protocol chip having storage for at least two SAS addresses and a method for selecting a single SAS address, and a processor unit connected to the SAS protocol chip by an interface bus, the processor configured to load two or more identifier addresses into the SAS protocol chip. The computer readable medium contains instructions that cause a processor to perform the described methods.