Two exactly the same Ultrastar HDDs - different speeds

When two identical Ultrastar hard disk drives (HDDs) show different performance speeds, it can be puzzling. Assuming both drives are the same model with identical specifications, such as capacity, cache size, and RPM, the discrepancy in performance may be due to several underlying factors. This article explores the most common reasons why two identical Ultrastar HDDs may deliver different speeds.

1. Interface and Connection Type

Even if both drives are the same model, the way they are connected to the system can impact performance. One drive may be connected via a SATA III (6Gbps) port, while the other could be on a slower SATA II (3Gbps) port. Similarly, differences in cable quality or length can also cause minor speed drops. Always ensure both drives are connected to high-speed ports with high-quality SATA cables.

2. Motherboard Configuration and BIOS Settings

The motherboard’s SATA controller settings can affect drive speed. If one drive is operating in AHCI mode and the other in IDE or RAID mode, their performance will vary. Check your BIOS/UEFI settings to ensure that both drives are using the same configuration. AHCI is recommended for optimal performance.

3. Drive Health and Age

Even if the drives are the same model, their internal health may differ. One drive may have developed bad sectors, higher reallocated sector counts, or higher power-on hours, all of which can degrade performance. Use tools like CrystalDiskInfo, HD Tune, or SMART data utilities to compare the health of both drives.

4. Firmware Differences

Hard drive manufacturers occasionally release firmware updates to improve performance or fix bugs. If one drive has a newer or different firmware version, it could perform slightly differently. You can check and update the firmware through the manufacturer’s website or tools.

5. System Load and Background Processes

The system environment where the drives are used can affect perceived speed. If one drive is connected to a machine with heavy background processes, antivirus scans, or fragmented files, it may appear slower. Ensure both systems (or the same system at different times) are under similar load conditions during testing.

6. Partitioning and File System Differences

The way a drive is formatted can influence performance. For example, a drive using NTFS with default cluster size may perform differently from one with a different file system or cluster configuration. Similarly, if one drive is nearly full or fragmented, read/write speeds may decrease.

7. Benchmarking Methodology

Inconsistent benchmarking tools or methods can also give misleading results. Different tools (e.g., CrystalDiskMark, ATTO, HD Tune) may show varying performance metrics based on how they test read/write speeds. Always use the same tool under the same conditions for both drives.

Conclusion

While it’s unusual, it’s not uncommon for two identical Ultrastar HDDs to exhibit different speeds. Factors like connection type, drive health, system load, firmware, and configuration differences can all contribute to this issue. A systematic check of each potential cause can help identify and resolve the discrepancy.