1.06 Troubleshoot and diagnose problems with storage drives and RAID arrays

Introduction

Imagine managing a critical server with a RAID 5 configuration, designed to protect valuable company data. One morning, you discover that the server is down, and the RAID configuration utility shows a "Volume Degraded—Disk Failure Detected" message.

Relieved that RAID 5 can handle one disk failure, you prepare to replace the disk. Suddenly, a second alert pops up: "Second Disk Failure Detected." The entire RAID array is now offline, and all essential data is inaccessible. Panic sets in—how do you recover the data, and what could have prevented this situation? This lesson will explore common failures and how to troubleshoot them to prevent data loss and minimize downtime. 

Types of Raid Failures 

RAID (Redundant Array of Independent Disks) is used to protect data by copying it to multiple drives or storing extra information to recover from failures, but RAID can still fail in different ways that need troubleshooting. 

Single Device Failure (Degraded State): 

  • When one disk in the RAID array fails, the array enters a degraded state. In this state, the RAID can still function, but its performance may be impacted, and it is no longer providing full redundancy. The specific impact depends on the RAID level: 

    • RAID 1 (Mirroring): If one disk fails, the data remains accessible because it is mirrored on another disk. 

    • RAID 5 (Striping with Parity): The data can still be reconstructed using parity information, but the array is at risk if another disk fails before the failed disk is replaced. 

    • RAID 6 (Striping with Double Parity): Two disk failures can be tolerated, but the array becomes vulnerable to additional failures. 

  • The degraded state is typically temporary until the failed disk is replaced, and the RAID array is rebuilt.  Rebuilding the array entails the process of restoring data onto a new disk after a failure in a RAID array. 

Multiple Device Failure:  When more than one disk fails in RAID levels that only provide redundancy for a single disk failure (such as RAID 1, RAID 5), the RAID array cannot recover, leading to a critical failure. This results in data loss unless additional backups are available. 

Entire RAID Volume Failure: 

  • This occurs when the entire RAID array becomes inaccessible or fails due to a serious issue, such as: 

    • Controller Failure: The RAID controller, which manages the array, can fail. If the controller fails, the entire RAID volume may become inaccessible, even if the disks themselves are still functional. 

    • Configuration Corruption: RAID configuration settings may become corrupted, causing the RAID array to fail to mount or be recognized by the system. 

    • Logical Failures: Corruption of the file system or data due to software errors, malware, or other logical issues can render the RAID volume unusable, despite the physical disks being intact. 

Data Loss or Corruption: 

  • Bit Rot or Data Corruption: Over time, small errors (bit rot) can accumulate on disks, potentially causing data corruption. RAID arrays, particularly those using parity (like RAID 5 or 6), can detect but may not always correct data corruption without additional measures like error correction codes (ECC). 

  •  Boot Process Issues: If the RAID volume fails to boot, use the RAID configuration utility to check the array status. If the utility isn't accessible, the RAID controller might be defective. 

Storage Drives 

Hard disk drives (HDDs) and solid-state drives (SSDs) can fail due to mechanical issues, power loss, or wear over time, and it's important to recognize the signs of potential failure to avoid data loss. 

  • Mechanical Noise (HDDs only): A healthy HDD makes low-level noise during operation, but loud or grinding noises, or clicking sounds, suggest mechanical problems and imminent failure. 

  • No LED Status Indicator Activity: If disk activity lights are inactive, it could mean the system is not receiving power, or the specific disk unit has failed. 

  • Constant LED Status Indicator Activity: Known as disk thrashing, this continuous activity might indicate insufficient system RAM, forcing the disk to handle virtual memory operations constantly. It can also signal a faulty software process or malware infection.

‘Disk thrashing’ is a performance issue that occurs when a computer’s operating system spends more time swapping data between RAM and the disk (virtual memory) than executing actual tasks. This happens when there is insufficient physical memory (RAM) to handle active processes, forcing the system to rely excessively on virtual memory. Virtual memory is stored on the hard disk, which is much slower than RAM. 

Key Characteristics of Disk Thrashing:

  • Excessive Disk Activity: The hard drive’s activity light remains on or flashes continuously.

  • System Slowness: Applications and the operating system respond very slowly or become unresponsive.

  • High CPU Usage: The CPU may appear busy, but it’s mostly waiting for data to load or save to disk.

  • Bootable Device Not Found: This message during boot-up means the fixed disk is either faulty or has corrupted files, preventing the operating system from loading. 

  • Missing Drives in OS: If a drive doesn't appear in system tools like File Explorer, check if it is initialized and formatted correctly. If not detected by disk management utilities, a hardware fault or a bad cable/connector might be the cause. 

  • Read/Write Failures: Errors such as "Cannot read from the source disk" suggest bad sectors (HDD) or bad blocks (SSD). HDD sectors can become damaged from power failures or mechanical faults, while SSD blocks degrade after many write operations. Tools like CHKDSK can help identify and monitor worsening conditions. 

  • Blue Screen of Death (BSOD): Severe read/write failures from a failing disk or file corruption can lead to a system crash and display a BSOD, indicating critical errors. 

When these symptoms appear, immediately back up all critical data and plan to replace the disk to prevent data loss and maintain system integrity. 

Analyzing Drive Health 

To troubleshoot drive reliability and performance, it's important to use both observation and diagnostic tools to identify issues with fixed disks like HDDs and SSDs. 

  • SMART Technology: Most fixed disks have a built-in self-diagnostic tool called SMART (Self-Monitoring, Analysis, and Reporting Technology) that alerts the operating system to potential failures. 

  • Advanced Diagnostics: If you suspect a drive is failing or notice performance issues like slow read/write times, run advanced diagnostics tests. These can be performed using utilities provided by the drive vendor or system diagnostics programs. 

  • Windows Utilities: You can also use Windows utilities to check SMART data and perform manual tests to assess drive health. 

  • Performance Metrics: Diagnostic tests provide statistics such as input/output operations per second (IOPS). If these metrics are below the vendor's baseline, the drive is likely faulty. If metrics match the benchmark, slow performance may be due to system issues like high application load, limited system resources, file fragmentation (for HDDs), or low remaining capacity. 

  • Bad Sectors and Blocks: Extended read/write times can also occur due to bad sectors (on HDDs) or blocks (on SSDs), leading to data loss or corruption. When detected, the disk firmware marks these as unavailable for future use. 

  • File Recovery: If a hard disk has file corruption and no backup is available, recovery utilities may help retrieve data. Recovery from an SSD is more challenging and often requires specialized tools. 

 

Summary 

Congratulations on completing this lesson on troubleshooting RAID arrays and storage drives! You've learned how RAID configurations protect data by using mirroring or parity, and how they can still fail due to various factors like disk failures or controller issues. You now know how to identify and address degraded states, replace failed disks, and rebuild arrays, as well as recognize common HDD and SSD failures, such as mechanical noise, read/write errors, and performance drops. Armed with this knowledge, you're ready to diagnose and solve drive issues effectively.