Disk-less Quorum Device Using NVRAM Bitmap for Clustered Storage
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Solution Overview
Problem
Clustered data storage systems face performance degradation due to the need for disk-based quorum devices, which incur high access times and network traffic, especially when handling write requests and maintaining NVLogs for redundancy.
Innovation Solution
Implementing a disk-less quorum device using non-volatile memory (NVRAM) to store write status information and pending operations, eliminating the need for NVLogs and reducing network communication between controllers, with a shared bitmap indicating write operation status for each storage block.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If disk-based quorum device is used to store write status information, then data integrity is maintained, but system throughput and performance decrease due to high access times
Solution Approach 1:
The patent changes the physical medium parameter from magnetic disk to solid-state NVRAM, which fundamentally alters the access time characteristic while maintaining data persistence. This parameter change resolves the contradiction by providing both data integrity (through non-volatility) and high performance (through solid-state speed).
2Reliability
If NVLogs are transmitted between controllers to share write request information, then failure protection is ensured, but network bandwidth consumption and processing load increase
Solution Approach 1:
The patent extracts the write status information from the controller memory and places it in a shared NVRAM location accessible by all controllers. This eliminates the need to transmit NVLogs between controllers, as each controller can directly read the write status from NVRAM, thus ensuring failure protection without the network overhead.
Solution Approach 2:
The patent introduces NVRAM as an intermediary storage medium that sits between the controllers and the quorum device. Instead of controllers communicating directly with each other through the network, they all interact with the shared NVRAM, which mediates the information exchange and eliminates network traffic for NVLog synchronization.
3Reliability
If disk-based quorum device is used, then quorum information is stored reliably, but access time increases and system performance decreases
Solution Approach 1:
The patent changes the storage medium parameter from slow magnetic disk to fast solid-state NVRAM, which simultaneously improves both reliability (data persistence) and access time performance, resolving the contradiction between these two requirements.
Data Source
AI summary
A disk-less quorum device in a clustered storage system includes non-volatile memory to store status information regarding the cluster and each storage controller in the cluster. The quorum device maintains a bitmap, shared by the controllers in the cluster, in the non-volatile memory. The bitmap indicates the status of a write operation to any data block or parity block. A “dirty” data unit in the bitmap indicates that a write operation has been submitted but is not yet finished. Upon submitting a write request (to update a data block or a parity block) to the storage facility, a controller sets the corresponding data unit “dirty” in the bitmap. After receiving an acknowledgement from the storage facility indicating that the operation has been completed, the controller clears the corresponding data unit. If a controller fails during a write operation, another controller can use the bitmap to re-establish data consistency.