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How to Read Hard Drive Power-On Hours & Start-Stop Counts

Updated · Standard formula, shown below

How to Read Hard Drive Power-On Hours & Start-Stop Counts

This guide shows you how to check a hard drive’s power-on hours (POH) and start-stop counts using S.M.A.R.T. data. These two numbers tell you how much the drive has been used and how often it has been cycled, which helps you estimate its remaining lifespan and spot potential issues before they cause data loss.

What You’ll Need

  • A Windows, macOS, or Linux computer with the target hard drive connected (internal or external via USB).
  • A S.M.A.R.T. reading tool. Free options include CrystalDiskInfo (Windows), smartctl (part of smartmontools, cross-platform), and Disk Utility (macOS, limited).
  • Administrator or root access to run the tools.

Step-by-Step

  1. Identify your drive model and interface. Check if it’s SATA, SAS, or NVMe. Most consumer drives are SATA; enterprise drives may be SAS. NVMe drives use a different S.M.A.R.T. structure, but power-on hours are still available.
  2. Download and install a S.M.A.R.T. tool. For Windows, CrystalDiskInfo is a simple GUI. For Linux or macOS, install smartmontools via your package manager (e.g., sudo apt install smartmontools on Ubuntu, brew install smartmontools on macOS).
  3. Run the tool with administrator privileges. On Windows, right-click CrystalDiskInfo and select “Run as administrator.” On Linux/macOS, use sudo in the terminal.
  4. Select the target drive. In CrystalDiskInfo, use the dropdown menu at the top to switch between drives. In smartctl, list drives with smartctl --scan.
  5. View the S.M.A.R.T. attributes. Look for the attributes labeled:
    • Power-On Hours (POH) – attribute ID 9. This shows total hours the drive has been powered on.
    • Start/Stop Count – attribute ID 4. This counts the number of times the drive has completed a full power cycle (spin-up and spin-down).
  6. Record the raw values. The raw value is the actual number. For example, a raw value of 12345 for POH means 12,345 hours. For Start/Stop Count, the raw value is the number of cycles.
  7. Interpret the values. A typical consumer drive is rated for 300,000–600,000 start/stop cycles, but that’s far more than most users will hit. Power-on hours are more relevant: a drive with 20,000+ hours (about 2.3 years of continuous use) is considered moderately used; 50,000+ hours is high. However, the specific model’s MTBF (mean time between failures) rating is a better reference.
  8. Check the health status. Most tools also show a health percentage or status (e.g., “Good” or “Caution”). This is based on other attributes like reallocated sectors, but if POH or start/stop counts are extremely high, the tool may flag it.

Common Mistakes

  • Confusing raw and normalized values. S.M.A.R.T. attributes have a normalized value (usually 100 or 200 at start) and a raw value. The raw value is the actual count; the normalized value is a health score that decreases over time. Always look at the raw value for POH and start/stop counts.
  • Using the wrong attribute ID. Some tools display attributes by name, but if you’re reading raw S.M.A.R.T. data, make sure you’re looking at ID 9 for POH and ID 4 for start/stop. For NVMe drives, the attribute names are different (e.g., “Power On Hours” is not in the same list), but the tool should translate them.
  • Ignoring the drive’s power-on cycles vs. start/stop. Some drives count a “load/unload” cycle separately from a full start/stop. The start/stop count is specifically for the spindle motor starting and stopping. Don’t mix them up.
  • Assuming the count is in days or years. Power-on hours are in hours, not days. A drive with 24/7 operation accumulates 8,760 hours per year.

Tips

  • Use the tool’s built-in warnings. CrystalDiskInfo and smartctl will often show a warning if the drive’s health is degrading. Even if POH is low, a high reallocated sector count is more concerning.
  • Check the drive’s rated lifespan. Look up the manufacturer’s datasheet for the specific model to find the rated POH and start/stop cycles. For example, a WD Red Plus might be rated for 550,000 load/unload cycles, but that’s not the same as start/stop.
  • Monitor trends over time. Run the check monthly and note the values. A sudden jump in start/stop counts could indicate a power supply issue or aggressive power-saving settings.
  • For external drives, use a USB-to-SATA adapter with S.M.A.R.T. passthrough. Some USB enclosures block S.M.A.R.T. data. If you see “No S.M.A.R.T. data,” try connecting the drive directly to a SATA port.

Troubleshooting

No S.M.A.R.T. data available. This can happen if the drive is connected via USB and the enclosure doesn’t support S.M.A.R.T. passthrough. Try a different enclosure or connect directly to the motherboard. On Linux, you may need to load the usb-storage module with the quirks parameter.

Tool doesn’t show the drive. Ensure the drive is properly detected in BIOS/UEFI. If it’s a new drive, initialize it in Disk Management (Windows) or Disk Utility (macOS) first. On Linux, check with lsblk.

smartctl returns “SMART support is disabled.” Run smartctl -s on /dev/sdX (replace sdX with your drive) to enable it. You may need to do this each boot or set it in BIOS.

Values seem impossibly high (e.g., POH in millions). Some drives have a bug where the raw value is a 32-bit number that overflows. In that case, look at the normalized value or use a different tool to cross-check.

Start/stop count is 0. Some SSDs don’t report this attribute. For SSDs, use “Power-On Hours” and “Power Cycles” instead. For HDDs, if it’s truly 0, the drive may be reporting incorrectly or the attribute is not supported.

Frequently Asked Questions

What is a good power-on hours count?

For a used drive, under 10,000 hours is light use, 10,000–30,000 is moderate, and over 50,000 is heavy. But the model’s rating matters more; a drive rated for 1 million hours MTBF can last much longer.

How many start/stop cycles is too many?

Most HDDs are rated for at least 50,000 start/stop cycles. If you see over 100,000, the drive may be nearing its design limit, but many drives exceed this without failure.

Can I reset the power-on hours counter?

No, not reliably. S.M.A.R.T. counters are stored in the drive’s firmware and cannot be reset by the user. Some tools claim to reset them, but they often only hide the data, and it will reappear.

Do SSDs have power-on hours?

Yes, SSDs also record power-on hours, but they don’t have start/stop counts in the same way. Instead, they track “power cycles” and “media wear.” The same S.M.A.R.T. tools show these.

Why does my drive show a different POH in different tools?

Some tools round the value or use different units (e.g., minutes vs. hours). Always check the unit label. Rarely, a tool may read the raw value incorrectly; cross-check with a second tool.

Is a high start/stop count more dangerous than high POH?

Not necessarily. Both contribute to wear, but the failure rate increases with both. A drive with 20,000 hours but only 100 start/stops is fine; a drive with 2,000 hours but 50,000 start/stops may be at risk due to mechanical stress.

Related

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.