Problem
A RAID controller battery or flash-backed cache module fails, forcing write-through mode and making sustained ingest dramatically slower.
Solution
Root Cause / Diagnostic:
Hardware RAID controllers utilize onboard DRAM cache to absorb high-speed write bursts. When the Battery Backup Unit (BBU) or CacheVault flash capacitor degrades below holding capacity, the controller automatically disables write-back caching and enters conservative write-through mode to prevent data loss upon power failure, slashing write speeds by 80–90%.
Actionable Fix:
1. Cache Battery / Supercapacitor Replacement: Replace the depleted BBU or flash-backed write cache (FBWC) module on the hardware RAID controller card.
2. Controller Cache Policy Verification: In the RAID controller management utility (e.g., MegaRAID Storage Manager / StorCLI), verify write policy resets from "Write Through" back to "Write Back".
3. Write Ingest Benchmark: Execute a 100GB sequential file write to verify that ingest throughput returns to full controller-accelerated speeds (>1500MB/s).
Pro Tip:
If your hardware RAID suddenly slows to a fraction of its normal write speed overnight, check your RAID card's battery; a dead cache battery automatically shuts off write caching for safety.
Hardware RAID controllers utilize onboard DRAM cache to absorb high-speed write bursts. When the Battery Backup Unit (BBU) or CacheVault flash capacitor degrades below holding capacity, the controller automatically disables write-back caching and enters conservative write-through mode to prevent data loss upon power failure, slashing write speeds by 80–90%.
Actionable Fix:
1. Cache Battery / Supercapacitor Replacement: Replace the depleted BBU or flash-backed write cache (FBWC) module on the hardware RAID controller card.
2. Controller Cache Policy Verification: In the RAID controller management utility (e.g., MegaRAID Storage Manager / StorCLI), verify write policy resets from "Write Through" back to "Write Back".
3. Write Ingest Benchmark: Execute a 100GB sequential file write to verify that ingest throughput returns to full controller-accelerated speeds (>1500MB/s).
Pro Tip:
If your hardware RAID suddenly slows to a fraction of its normal write speed overnight, check your RAID card's battery; a dead cache battery automatically shuts off write caching for safety.