Scrub and SMART Testing Schedules for FreeNAS

This guide will follow this form how-to guide in the iX Community forms. My goal with this article is to make the steps a bit easier to read.

I also recommend the video below. Chris Titus Tech gives a very good explanation. He has a different schedule than below. But that is purely preference. Both are good.

What drives to run tasks on

SMART tests only need to be run on HDDs.

Scrub task should be ran on all of your drives besides the Boot Drive, the SATA DOM or USB.

Lifeline - Scrubs

Scrubs are your "regular maintenance for zpools.

They can take a few minutes to a few days depedning on:

  1. The size of your pool
  2. The performance of your pool
  3. Your pools storage history
  4. The performance of your system asa whole
  5. The workload placed on your pool during the scrub

Lifeline - SMART tests

SMART tests are interal drive tests

There is no ‘criteria’ for what is or is not done during a particular test. Each manufacturer has their own specifications for defines a short test or a long test.

Generally short tests late less than 5 minutes and long tests take hours. 

A long test usually read the entire platter to check for errors and short tests do a very simple quick test.


Do not schedule SMART tests at the same time as scrubs!

This will potentially overload the system.

More about SMART tests

SMART tests are non-destructive. So you can run them as often as you want. You can only run one test at a time per disk.

SMART tests do not return a final result. Rather it will email you if a SMART test fails. You will need to set up your email, and check it! No email means everything is good.

Your average dish will store the last 20 or so test results. So if you do tests at a very high frequency and one test fails, it may be removed from the log before you can examine it closely.

Some Notes about Scrubs

Scrubs are pretty hard on disks. So schedule them at a frequency that makes you comfortable with your pool.

SMART Monitoring VS SMART Testing

SMART Monitoring only monitors the drive in a way that finds errors that appear through regular use.

Smart Testing actually runs tests.

No Need For These Tests on SSDs

According to the form this article is based on, these tests are not needed on SSDs. If you have more information about this. Please leave a comment below.

The Scrub and Smart Test Schedule

This schedule comes from this form user. He uses this for a home server and is not concered about the preformance penalty because his pool preformes more than adequately even during a Scrub.

SCRUBS: 1st and 15th of the month at 4:00am. Threshold is set to 10 days.

Short SMART Test: Every 5th, 12th, 19th, and 26th of the month at 3:00 am

Long SMART Test: Every 8th and 22nd at 4:00 am

Short SMART Test Alternitive

If you want to do more short SMART tests you can choose to do every odd or every even day. Be sure to choose a time for your SMART test that does not interfere with a scrub or long test.

For example. In the schedule above, scrubs are scheduled at 4:00 am and the short SMART tests are scheduled for 3:00 am. Take note, the short SMART test only takes a few minutes to complete on a high preforming system. So these tests would not interfere. 

Be sure to check the time your system takes to complete tests and leave enough time between tests.

Do not run tests after the 28th

This is because the shortest month, Febuary, only has 28 days. If you had tests scheduled for the 29th, that test would not take place until the next scheduled day.

These rules are not set in stone.

You can run tests that fit your style and needs. Just don’t run the tests at the same time and be aware that running many Scrubs on your drives will shorten the life of your drives.

Checking Test Logs

Use the command below to see what tests have been completed and when. Some brands will not actually provide an entry until a test completes or fails

# smartctl -a /dev/da1

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