How do I troubleshoot a slow hard drive?

Checking the S.M.A.R.T. attributes is a useful at-a-glance first step to identifying hard drive issues.

Accessing S.M.A.R.T. Attributes

You can view S.M.A.R.T. attributes on Windows using third-party tools such as GSmartControl.

On macOS, you can use Disk Utility, though it isn't very verbose. You can install smartctl from the package smartmontools to access the S.M.A.R.T. attributes using the command line.

On Linux, the command smartctl -a /dev/hda (from the package smartmontools) gives S.M.A.R.T. information about a hard drive, where /dev/hda is replaced with the device in question. GNOME Disks (gnome-disks from the package gnome-disk-utility, previously known as palimpsest) is a graphical utility that can give some more advice about the condition of your hard drive.

Understanding S.M.A.R.T. Attributes

Here are some attributes that are relevant and worth noting. A larger list can be found here.

A non-zero Read Error Rate (ID 1) indicates a problem with either the disk surface or the read/write heads.

The Throughput Performance (ID 2) is the average efficiency of the disk. If the value drops below the threshold, something may be wrong with the disk.

A high Spin-Up Time (ID 3) (recorded in milliseconds) may indicate that the hard drive is having trouble spinning up.

An increasing Reallocated Sectors Count (ID 5) means that areas on the hard drive are failing in integrity, and data had to be moved. This causes performance decreases when sectors are being remapped, but it may be more serious in that the hard drive is about to fail.

A low Seek Time Performance (ID 8) is a sign of a mechanical issue with the magnetic heads.

The Spin Retry Count (ID 10) goes up when a spin-up fails. If this happens, input/output operations are queued until the hard drive can spin normally, which causes slowdowns. More importantly, though, if the hard drive has to retry spinning up, it's a sign of imminent failure.

A non-zero Reported Uncorrectable Errors (ID 187) count means that that number of sectors could not be corrected by hardware error correction. Here's a sign of old age.

The Current Pending Sector Count (ID 197) is the number of sectors waiting to be remapped. This indicates old age of the hard drive.

HDD Benchmarks

If there's a certain location in the hard drive that is getting poor performance (maybe where frequently used information is stored), hard drive read benchmarks can help confirm this. Above is a screenshot of a hard drive benchmark using palimpsest, now known as GNOME Disks (gnome-disks).

If you prefer to do command line benchmarks on Linux, you can combine multiple options:

• hdparm (from the package hdparm)
  • hdparm -t /dev/hda — Buffered sequential read test on /dev/hda
  • hdparm -T /dev/hda — Cached sequential read test on /dev/hda
• dd (from the package coreutils)
  • dd if=/dev/hda of=/dev/zero bs=1M count=1024 — Sustain a read from the beginning of /dev/hda for 1GiB using a block size of 1MiB
• ioping (from the package ioping)
  • ioping -R /dev/hda — Random read test on /dev/hda

On Windows, you can use tools like HD Tune to do hard drive benchmarks.

On macOS, you can use tools like Blackmagic Disk Speed Test to do hard drive benchmarks.

Another way you can test within Windows is to run the Command Prompt (Run as Administrator in Vista or Windows 7). From there, type CHKDSK C: /f /r and press Enter. This will scan the file system, and the free space for errors

Check your drives S.M.A.R.T. status with a tool like GSmartControl. If there are serious problems like defective sectors, these are probably visible in the data. You can also launch a self-test to find out about new errors, that haven't been logged yet.