Early Warning of Fail-Slow Events

In the fast-paced realm of modern Data Centers and IT infrastructure, ensuring the reliability and performance of storage components is crucial for seamless operations. Failures, especially the elusive and degrading "fail-slow" events, can significantly impact system efficiency and application responsiveness. Enter SMARTDriveAI, a SaaS based AI and analytics monitoring service that has emerged as a valuable early warning solution against disruptive fail-slow conditions in all types of drives, including NVMe SSDs, SATA/SAS SSDs, and HDDs, and RAID based file systems. Drawing insights from comprehensive studies by the major hyperscaler Data Centers, this article delves into the use of SMARTDriveAI and its role in preemptively identifying and addressing fail-slow events.

Understanding Fail-Slow: A Statistical Overview

Fail-slow is a phenomenon wherein drives exhibit gradual performance deterioration over time, resulting in increased latencies and decreased responsiveness. This performance deterioration can be short or long lived. The performance degradation is usually enough to affect many applications, giving rise to instability that produces enough delay to lead to violations in application service level objectives (SLO), degrading user experience. The attached paper, "NVMe SSD Failures in the Field: the Fail-Stop and the Fail-Slow," is one of many that provides a wealth of data to underscore the prominence and impact of fail-slow events. The paper highlights Alibaba's experience in managing over 1.8 million NVMe SSDs in several Data Centers.

Key Observations from the Paper

  • Fail-Slow events are more widespread in NVMe SSDs: unlike earlier studies on traditional SAS/SATA SSDs, the presentation reveals that NVMe SSDs experience a higher incidence of fail-slow events
  • Fail-slow events in NVMe SSDs are much more widespread and frequent compared to HDDs and can degrade the drive to SATA SSD or even HDD level performance
  • Frequency and duration: fail-slow event frequency in NVMe SSDs is 7-69X higher than in HDDs. Event durations are 19-52X longer in NVMe SSDs versus HDDs.
  • If a fail-slow drive is part of a RAID set, the entire RAID set can perform poorly

While definitive causes for fail-slow events can be elusive, several factors have been identified as potential contributors:

    NVMe SSDs

  • Garbage Collection Activities: The SSD controller's periodic garbage collection can interfere with host operations and lead to increased latencies.
  • NAND Wearout: Deterioration of NAND flash cells with usage can lead to reduced read/write performance and prolonged latencies.
  • Controller Firmware Bugs: Firmware glitches can trigger performance disruptions, affecting the drive's responsiveness.
  • Background Maintenance: Internal tasks such as data refreshing may compete with host operations, impacting overall drive performance.
  • Thermal Throttling: Elevated temperatures can prompt SSD controllers to throttle performance, further exacerbating latency issues.

    HDDs:

  • Mechanical Failures: Mechanical issues like bad sectors, platter damage, or head failures result in increased seek times and latency.
  • Wear of Moving Parts: Gradual wear of critical components like heads, platters, motors, and bearings can lead to performance degradation.
  • Workload Interference: Background tasks such as defragmentation and error recovery can impede host operations and responsiveness.
  • Thermal Throttling: High temperatures can trigger throttling in HDDs, causing latency spikes.

Reinforcing Reliability: SMARTDriveAI's Role

SMARTDriveAI steps onto the stage as a proactive safeguard against the disruptive impact of fail-slow events. By continuously monitoring both file systems and drives, SMARTDriveAI possesses the capability to detect subtle performance degradation indicative of fail-slow conditions. Leveraging its advanced analytics and machine learning models, SMARTDriveAI compares the behavior of individual drives within a server, identifying those that consistently exhibit latency beyond the statistical norm and then proactively notifies IT operations of any anomalies. Since fail-slow durations can be minutes to several days in length, the trend information SMARTDriveAI collects can be of great use in viewing the life cycle of fail-slow events and the affect on colocated drives and file systems.

Operational Advice

The article states that Alibaba has implemented fail-slow policies that are a compromise based on cost, since few of the fail-slow drives become fail-stop failures. The first time a drive is diagnosed with a fail-slow failure, the drive's data is cleaned and the drive is deployed again as a new drive. The second time a fail-slow event is diagnosed, Alibaba fully flushes the drive with zeros, reformats and redeploys it. The third time the drive is put offline and replaced. It's interesting that of the drives sent back to the vendor for repair, 33% had bad capacitors and 46% contained bad chips. The root causes for the remaining drives were unclear. The important lesson is the fast identification of the fail-slow event so mitigation can start immediately. Note that the drives discussed here were not part of a RAID set. Replacing drives in a RAID set can be very disruptive and requires alternate replacement policies.

Conclusion

SMARTDriveAI's use as a proactive monitoring solution marks a pivotal advancement in tackling the complex and pervasive challenges posed by fail-slow conditions. The insights gleaned from industry experience by the hyperscalers underscore the alarming prevalence of these events, particularly in the realm of NVMe SSDs. By harnessing SMARTDriveAI's built in AI and analytics capabilities, IT infrastructure stakeholders can proactively detect and mitigate issues caused by fail-slow conditions, ensuring continued system reliability and optimal performance. As technology continues to evolve, the strategic embrace of solutions like SMARTDriveAI becomes imperative for fortifying the foundations of our digital ecosystem against the subtler threats that can undermine its integrity.

Paper referenced: "NVMe SSD Failures in the Field: the Fail-Stop and the Fail-Slow" by Alibaba. https://www.usenix.org/conference/atc22/presentation/lu