How to Monitor Your NAS’s Health and Catch Drive Failures Early
12 min read
2,395 words
If you own a NAS, your drives will fail eventually. The question is whether you find out about it when a SMART attribute crosses a threshold, or when the array degrades and you lose redundancy. This guide walks through exactly how to monitor your NAS’s health — from the SMART attributes that actually matter, to setting up automated alerts, to third-party dashboards that beat staring at raw smartctl output.
You will learn how to run SMART self-tests through both GUI tools (Synology DSM, TrueNAS Scale) and the command line, which attributes reliably predict failure, and how to combine drive monitoring with RAID and backup so no single layer is your only defense.
What Is SMART Monitoring and Which Attributes Actually Matter for Your NAS?
SMART (Self-Monitoring, Analysis, and Reporting Technology) is a built-in system on modern hard drives and SSDs that tracks dozens of internal attributes. The drive monitors itself continuously — vibration, temperature, read error rates, reallocated sectors — and stores the data in firmware-accessible registers. Your NAS or server can read these registers and report them back to you.
Not all SMART attributes are equally useful for predicting failure. Drive manufacturers expose 40–60 attributes, but only a handful correlate strongly with imminent failure.
| SMART Attribute | What It Measures | Why It Matters for Your NAS |
|---|---|---|
| Reallocated Sector Count (ID 5) | Number of bad sectors remapped to spare area | Rising values almost always indicate a failing drive. A single reallocated sector is not immediate death, but a trend upward means replace soon. |
| Current Pending Sector Count (ID 197) | Sectors that cannot be read and are candidates for reallocation | Any non-zero value means the drive is struggling to read data. This often precedes reallocated sectors and data loss. |
| Uncorrectable Sector Count (ID 198) | Sectors that failed reallocation and are completely unrecoverable | Any non-zero value means you have already lost data on that sector. Replace the drive immediately. |
| Temperature (ID 194) | Drive temperature in Celsius | Sustained temps above 45-50°C accelerate bearing wear and reduce lifespan. Most consumer drives operate best at 30-40°C. |
| Power-On Hours (ID 9) | Total hours the drive has been powered on | Useful for lifespan estimation. Most drives are rated for 300,000-500,000 hours (34-57 years continuous), but failure rates rise after 3-5 years of 24/7 operation. |
Focus on attributes 5, 197, and 198. A single reallocated sector on a 5-year-old drive is a strong signal to start planning a replacement. On a brand-new drive, it may be a manufacturing defect — run a long SMART test and consider an RMA.
How to Check Hard Drive Health on Your NAS Using the GUI
Every major NAS operating system includes built-in SMART monitoring. The GUI approach is the easiest way to get started if you are not comfortable with the command line.
Synology DSM: Storage Manager → HDD/SSD → Health Info
Open Storage Manager, select the HDD/SSD tab, and click on any drive. The Health Info section shows the overall SMART status (Passed or Failed) and lists individual attribute values. DSM runs a short SMART test automatically every week by default and a long test every month. You can also trigger a manual test from the Action menu.
Synology’s DSM also shows a “Health Status” percentage that combines SMART data with drive age and historical performance. This is a useful at-a-glance indicator but should not replace checking raw attribute values — especially reallocated sector counts.
TrueNAS Scale: Storage → Disks → SMART
In TrueNAS Scale, navigate to Storage, click Disks, then select a specific disk. The SMART Tests section shows past test results and allows you to run short, long, or conveyance tests immediately. TrueNAS also supports automated SMART test schedules — set a short test daily and a long test weekly for each drive.
For TrueNAS Core (FreeBSD-based), the process is similar under Storage → Disks → SMART Tests. The underlying tool is the same smartctl utility, just wrapped in a web interface.
If you are deciding between these two operating systems, you can read our detailed comparison: TrueNAS vs Unraid: Which Should You Run in 2026?
Running SMART Tests via Command Line (smartctl) for Maximum Control
The smartctl command, part of the smartmontools package, gives you direct access to every SMART attribute and test type. It works on any Linux, FreeBSD, or macOS system and is the fallback when a GUI is not available or when you need more detail.
On Debian/Ubuntu: sudo apt install smartmontools. On FreeBSD: pkg install smartmontools. Most NAS OSes include it by default.
Run sudo smartctl -i /dev/sda (replace sda with your drive). Look for “SMART support is: Enabled.” If it says Disabled, run sudo smartctl -s on /dev/sda to enable it.
Run sudo smartctl -A /dev/sda. This prints every attribute with its current, worst, threshold, and raw values. Focus on ID 5, 197, and 198.
sudo smartctl -t short /dev/sda. This takes about 2 minutes and checks the drive surface and electronics. Wait for completion, then check results with sudo smartctl -l selftest /dev/sda.
sudo smartctl -t long /dev/sda. This can take 4-12 hours depending on drive size and performs a full surface scan. Run it monthly on each drive.
A long SMART test stresses the drive and can cause noticeable performance degradation on a busy NAS. Schedule it during low-usage hours, such as overnight or on weekends. Do not run long tests on all drives simultaneously in a RAID array — the I/O load can cause timeouts.
Setting Up Automated Alerts to Predict Drive Failure Before It Happens
Manually checking SMART attributes every week is better than nothing, but automated alerts are what actually save you from data loss. The goal is to get an email or notification the moment a critical attribute crosses a threshold — not days later when you happen to check the dashboard.
Configuring Alerts in Synology DSM
Go to Control Panel → Notification → Advanced. Enable “Send notifications when a storage volume degrades or crashes” and “Send notifications when a SMART test fails.” You can set up email, SMS, or push notifications via the Synology QuickConnect app. DSM also supports SNMP traps for enterprise monitoring systems.
Configuring Alerts in TrueNAS Scale
Navigate to System Settings → Alert Settings. TrueNAS Scale sends alerts for SMART test failures, drive temperature thresholds, and ZFS pool degradation by default. You can customize thresholds under Storage → Disks → Edit Disk → SMART Options. Set the temperature threshold to 45°C for HDDs and 60°C for SSDs.
Setting Up smartd for Custom Alerts on Any Linux System
The smartd daemon runs in the background and monitors drives continuously. Edit /etc/smartd.conf and add a line like this:
/dev/sda -a -o on -S on -s (S/../.././02|L/../../7/03) -m youremail@example.com -M test
This line enables all monitoring, schedules a short test daily at 2 AM and a long test weekly on Sunday at 3 AM, and emails you on any SMART failure. The -M test flag sends a test email immediately so you know the config works.
Third-Party Tools for a Friendlier SMART Dashboard
If you find raw smartctl output hard to parse or want historical trend charts, third-party tools give you a web-based dashboard with graphs, email alerts, and multi-drive views.
| Tool | Best For | Key Features | Cost |
|---|---|---|---|
| Scrutiny | Docker-based homelabs | Web UI with historical graphs, email/webhook alerts, supports any smartctl-compatible drive | Free (open-source) |
| HD Sentinel | Windows-based NAS or single-server setups | Detailed health percentage, temperature logging, performance benchmarks | $30-$60 (paid) |
| Grafana + Prometheus + smartctl exporter | Advanced homelabs with existing monitoring stack | Custom dashboards, alerting rules, long-term storage of SMART metrics | Free (open-source) |
| QNAP QTS Storage Manager | QNAP NAS owners | Built-in SMART tests, drive health status, email alerts | Included with QNAP OS |
Scrutiny is the most popular option for homelab users running Docker. It auto-discovers drives on the host system, runs scheduled tests, and presents a clean web interface with color-coded health status. You can run it in a single Docker container on any Linux host or NAS that supports Docker.
For those running TrueNAS or Unraid, Scrutiny integrates well — but note that TrueNAS already includes robust SMART monitoring. If you already have a Best CPU for TrueNAS in 2026: From Basic NAS to ZFS Powerhouse setup, the built-in tools may be sufficient. Scrutiny is most valuable when you want historical graphs that go beyond the “Passed/Failed” binary.
Combining SMART Monitoring with RAID and Backups
SMART monitoring is one layer of a multi-layer data protection strategy. It cannot do everything.
What SMART Monitoring Protects Against
- Gradual drive degradation (increasing reallocated sectors)
- Temperature-related failures
- Mechanical wear visible in power-on hours
- Predictable failures that develop over days or weeks
What SMART Monitoring Cannot Protect Against
- Sudden catastrophic drive failure (head crash, electronics failure)
- Accidental file deletion or ransomware
- Fire, flood, or theft of the NAS
- RAID controller or cable faults
RAID provides redundancy against drive failure — RAID 5 tolerates one drive failure, RAID 6 tolerates two. But RAID is not a backup. If you delete a file by accident or ransomware encrypts your shares, RAID does nothing to help. You need a separate backup to an external drive, a second NAS, or cloud storage.
SMART monitoring fills the gap between “drive is fine” and “drive has failed.” It gives you early warning so you can replace a degrading drive while the RAID array is still healthy. Without SMART monitoring, you might not know a drive is failing until it drops out of the array, at which point you are rebuilding on degraded hardware — a risky scenario.
For a deeper dive into RAID levels and usable storage, see our guide: RAID 1 vs RAID 5: Which Gives You More Usable Storage?
A common mistake is relying solely on SMART self-tests without checking attribute values between tests. A drive can accumulate thousands of reallocated sectors during normal operation but still pass a short self-test because the test only reads a small portion of the surface. Always check raw attribute values (smartctl -A) weekly, not just test results.
Which Monitoring Approach Should You Choose for Your NAS?
The right approach depends on your NAS operating system and your comfort level with the command line.
- Use the built-in GUI if you run Synology DSM, TrueNAS Scale, or QNAP QTS. These interfaces show SMART attributes, run automated tests, and send email alerts out of the box.
- Use smartctl directly if you run a custom Linux server, Proxmox, or Unraid and want full control over test schedules and attribute thresholds.
- Add a third-party dashboard (Scrutiny) if you want historical graphs across multiple drives and a single pane of glass for all your storage health.
- Always combine with RAID and backups. SMART monitoring tells you when to replace a drive. RAID keeps the data safe during the replacement. Backups protect against everything else.
Start by enabling SMART monitoring today — even if you only check attributes once a week manually, it is infinitely better than waiting for a drive to fail silently. Set up automated alerts within the first week, and schedule long self-tests monthly. Your future self will thank you when a SMART alert catches a failing drive before your array degrades.
If you are planning a new NAS build, consider how drive selection affects your monitoring strategy. Larger drives take longer to run long SMART tests, and drives with helium filling tend to show different failure patterns than air-filled drives. For storage sizing guidance, see: How Much Storage Do You Need for a NAS? A Practical Sizing Guide
Frequently Asked Questions
What SMART attributes should I actually worry about?
Focus on three attributes: Reallocated Sector Count (ID 5), Current Pending Sector Count (ID 197), and Uncorrectable Sector Count (ID 198). A rising value on any of these is a strong indicator of impending failure. Temperature (ID 194) is also important — sustained readings above 45°C for HDDs or 60°C for SSDs shorten drive lifespan. Power-On Hours (ID 9) helps estimate age but is not a direct failure predictor. Ignore raw read error rate and seek error rate attributes, as they vary widely between manufacturers and often show high values on healthy drives.
How do I run a SMART test on my NAS?
On Synology DSM, open Storage Manager, select the HDD/SSD tab, click a drive, and choose Action → SMART Test → Short or Long. On TrueNAS Scale, go to Storage → Disks, select a disk, and click Run Test under SMART Tests. On the command line, use sudo smartctl -t short /dev/sda for a quick test (about 2 minutes) or sudo smartctl -t long /dev/sda for a full surface scan (4-12 hours depending on drive size). Check results with sudo smartctl -l selftest /dev/sda. Schedule short tests daily and long tests weekly or monthly for optimal coverage.
Can SMART monitoring predict a drive failure before it happens?
SMART monitoring can predict about 50-74% of drive failures, depending on the study and drive type. Backblaze’s long-term data shows that drives with a high Reallocated Sector Count (ID 5) are 15-20 times more likely to fail within 60 days than drives with zero reallocated sectors. However, SMART cannot predict sudden catastrophic failures caused by head crashes, power surges, or controller electronics failure. This is why you should never rely solely on SMART monitoring — combine it with RAID redundancy and a separate backup strategy for complete data protection.
What tools give a friendlier SMART dashboard than the command line?
Scrutiny is the most popular open-source option for homelab users. It runs in Docker, auto-discovers drives, and provides a web dashboard with historical graphs, email alerts, and color-coded health status. HD Sentinel is a paid alternative ($30-$60) that offers a detailed health percentage, temperature logging, and performance benchmarks — best for Windows-based setups. If you already run Grafana and Prometheus, you can export SMART metrics using the smartctl exporter and build custom dashboards. For most NAS users, the built-in GUI in Synology DSM or TrueNAS Scale is sufficient and requires no additional tools.
Last verified: July 09, 2026. SMART attribute behavior cross-checked against Backblaze hard drive failure statistics (2024-2026), smartmontools documentation, TrueNAS Scale 24.10 documentation, and Synology DSM 7.2 documentation.
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HomeLabCost editor covering NAS builds, hardware selection, and homelab server setup guides.