Disk-Initiated Asynchronous Event Notification in SAS Storage
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Solution Overview
Problem
Current information handling systems face performance degradation and increased design complexity due to disk polling in large storage systems, as existing technologies do not allow for disk-initiated asynchronous event notifications, leading to inefficient use of time slots in in-band communications protocols.
Innovation Solution
A SAS target device can initiate an asynchronous event notification (AEN) transaction using an AEN timer and out-of-band (OOB) mechanisms, allowing for disk-initiated communication to a host controller without requiring major changes to the RAID stack, thereby reducing the need for frequent polling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If disk polling is implemented in large storage systems, then disk events can be detected, but system performance degrades and design complexity increases
Solution Approach 1:
Instead of the host controller polling disks to detect events (traditional approach), the invention enables disks to autonomously initiate AEN transactions to notify the host controller of events. This inversion of the notification initiative fundamentally resolves the performance degradation caused by frequent polling in large storage systems.
Solution Approach 2:
The disk devices are empowered to self-notify the host controller of events without requiring external polling. By implementing autonomous event notification capability in the disks themselves, the system eliminates the need for continuous host-initiated polling, thereby improving overall system performance while maintaining reliable event detection.
2Reliability
If disk polling is implemented in large storage systems, then disk events can be detected, but design complexity increases
Solution Approach 1:
The invention inverts the traditional polling architecture by enabling disks to initiate notifications autonomously. This approach simplifies the host controller's role while adding minimal complexity to disk devices, as the disks already possess the capability to generate interrupt requests and communicate events through existing SAS protocol mechanisms.
3Loss of time
If AEN transactions are initiated by SAS target devices, then polling time is reduced, but this contradicts conventional SAS architecture where disks are targets only
Solution Approach 1:
The invention extends the AEN capability to SAS target devices (disks), making them multi-functional by enabling both traditional target operations and autonomous initiator functionality for event notification. This universal approach allows disks to perform dual roles without compromising their primary function, thereby reducing polling time while maintaining architecture compatibility.
Solution Approach 2:
The invention uses the existing SAS protocol framework and communication mechanisms as an intermediary to enable disk-initiated AEN transactions. By leveraging established protocol structures and communication pathways, the system allows disks to initiate notifications without requiring fundamental architectural changes, thus bridging the gap between traditional SAS design and new event notification capabilities.
Data Source
AI summary
A SAS target device, e.g., SAS disk, may instantiate an asynchronous event notification (AEN) transaction while still conforming to SAS protocol standards. When the SAS target has an event queued up for notification to a host controller but there is no host initiated communication going on for the SAS target to attach the notification, then the SAS target may start an AEN timer. If the AEN timer expires and the AEN is still pending, then a request is made to the SAS target to notify the host controller using a SAS PHY level out of band (OOB) mechanism. The OOB message may be sent via a new OOB signal or by sending a COMINIT signal from the SAS disk PHY, requiring a link reset and then using a bit in an IDENTIFY frame for the pending AEN. Receiving and issuing an AEN may then be communicated during PHY initialization.