Extremely slow hard drive random 4k reads (and only 4k reads). Even slower than 5400rpm drive.

Understanding the Paradox of Slow Random 4K Reads on Higher-RPM Enterprise Hard Drives

An In-Depth Analysis of Unexpected Drive Performance and Troubleshooting Strategies

Introduction

In the realm of data storage, drive performance metrics often influence purchasing decisions and deployment strategies. However, practitioners sometimes encounter peculiar performance anomalies that challenge conventional expectations. One such perplexing scenario involves the use of high-capacity, 7200 RPM enterprise-grade hard drives exhibiting unexpectedly sluggish random 4K read speeds—sometimes even performing worse than traditional 5400 RPM drives. This article explores this phenomenon, provides insights into potential causes, and discusses effective troubleshooting methods.

The Situation

Imagine setting up a data storage system using refurbished Western Digital Ultrastar DC HC530 drives—14TB, 7200 RPM, enterprise-class SATA HDDs. Despite their advanced specifications, these drives show extremely low random 4K read speeds in benchmarking tests, significantly underperforming compared to older, slower drives like a 4TB WD Blue WD40EFRX at 5400 RPM.

Sample Benchmark Results

| Test | WD 14TB Ultrastar (O) | WD 14TB Ultrastar (P) | 4TB WD Blue (Older Drive) |
|————-|————————|————————|—————————|
| Sequential Read (Q8) | ~282 MB/s | ~265 MB/s | ~179 MB/s |
| Random 4K Q1 T1 | 0.14 MB/s | 0.14 MB/s | 0.55 MB/s |
| Random 4K Q32 T1 | ~3.2 MB/s | ~3.2 MB/s | ~2.4 MB/s |

Note: The extremely low random 4K read speeds (around 0.14 MB/s) raise questions about drive performance in random workload scenarios, which are typical in server environments and multitasking situations.

Potential Causes

Understanding this anomaly requires examining several factors:

Drive Configuration and Firmware

While enterprise drives are optimized for high workloads and durability, firmware settings or misconfigurations can impact performance, especially with respect to cache management and power modes.