RAID 5 Drive Failure Recovery: Step-by-Step Guide for Database Servers with Hardware Controllers


8 views

When a drive fails in a RAID 5 array with a hardware controller, you're operating in a degraded state. The system remains functional due to parity data, but performance typically suffers because:

  • Read operations require parity calculations
  • Write operations trigger full stripe rewrites
  • The controller works harder to reconstruct missing data

Before swapping the failed drive:


# Check current RAID status (Linux example)
cat /proc/mdstat

# Or for hardware controllers (adapt for your vendor)
megacli -LDInfo -Lall -aAll

Key precautions:

  • Backup critical data immediately (even in degraded state)
  • Document your RAID controller model and firmware version
  • Prepare the exact replacement drive model if possible

With a hardware RAID controller, the rebuild is typically automatic:

  1. Physically replace the failed drive (hot-swap if supported)
  2. The controller should detect the new drive automatically
  3. Most controllers will begin rebuilding immediately

For specific controllers like PERC (Dell) or MegaRAID (LSI):


# MegaRAID CLI example to start rebuild
megacli -PdReplaceMissing -PhysDrv[E:S] -ArrayN -rowN -aN

# Check rebuild progress
megacli -PDRbld -ShowProg -PhysDrv[E:S] -aN

The slow performance you're experiencing is normal during:

  • The degraded state (pre-replacement)
  • The rebuild process (post-replacement)

Performance impact factors:

Factor Impact
Array Size Larger arrays take longer
Drive Speed SSDs rebuild faster than HDDs
Controller Cache BBU/cache helps performance

If automatic rebuild doesn't initiate:


# For Linux software RAID
mdadm --manage /dev/md0 --add /dev/sdX1

# For HP SmartArray controllers
hpacucli controller slot=0 array A modify drives=all

Critical notes:

  • Never reboot during rebuild unless absolutely necessary
  • Monitor SMART data on surviving drives
  • Consider scheduling rebuilds during low-usage periods

When a drive fails in a RAID 5 array with a hardware controller, the system enters a degraded state. Your observation about slow performance is expected - here's why:

// Pseudocode showing RAID 5 read operation during degradation
function readDataDuringDegradation(logicalBlockAddress) {
    if (requestedBlockIsOnFailedDrive) {
        // Reconstruct data using parity and remaining drives
        return xor(drive1Block, drive2Block); 
    } else {
        return directReadFromHealthyDrive();
    }
    // This reconstruction overhead causes performance impact
}

While waiting for the replacement drive:

  • Monitor the remaining drives' SMART status
  • Reduce write operations if possible
  • Take a full backup if the system permits

Example SMART monitoring command (Linux):

smartctl -a /dev/sda | grep -i "reallocated\|pending\|uncorrectable"

Most hardware RAID controllers follow this general workflow:

# Typical hardware RAID CLI commands (adapt to your controller)
# 1. Identify the failed drive (example from MegaCLI)
MegaCli -PDList -aAll | grep -i "firmware state"

# 2. Physically replace the drive (ensure proper slot matching)

# 3. Mark the new drive as a hot spare (if needed)
MegaCli -PDHSP -Set -PhysDrv[32:2] -a0

# 4. Initiate rebuild (varies by controller)
MegaCli -PDRbld -Start -PhysDrv[32:2] -a0

Rebuild times vary based on:

  • Drive capacity (larger drives take longer)
  • Controller performance
  • System workload during rebuild

Example rebuild monitoring command:

watch -n 60 "MegaCli -PDRbld -ShowProg -PhysDrv[32:2] -a0"

After successful rebuild:

# Check array status
MegaCli -LDInfo -Lall -aAll | grep -i "state"

# Perform a consistency check (if supported)
MegaCli -LDCC -Start -Lall -aAll

Remember to update your monitoring systems with the new drive's identifier.