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Monitors drive I/O and forces HDD spindown after a given idle period. Resistant to S.M.A.R.T. reads.

Disk spindown has always been an issue for various FreeNAS / TrueNAS users. This script utilizes iostat to detect I/O operations (reads, writes) on each disk. If a disk didn't receive reads or writes for a given period of time it is considered idle and gets spun down.

This excludes periodic reads of S.M.A.R.T. data performed by the smartctl service which therefore enables users to have S.M.A.R.T. reporting turned on while still being able to automatically spin down disks. The script also is immune to the periodic disk temperature reads in newer versions of FreeNAS / TrueNAS.

Currently successfully tested on: TrueNAS-12.0-U1.1 (Core), FreeNAS-11.3-U5, and FreeNAS-11.2-U7`.

Key Features

  • Periodic S.M.A.R.T. reads don't reset the idle timers
  • Configurable idle timeout and poll interval
  • Support for ATA and SCSI devices
  • Per-disk idle timer / Independent spindown
  • Automatic detection or explicit listing of drives to monitor
  • Ignoring of specific drives (e.g. SSD with system dataset)
  • Runnable via Tasks as Post-Init Script, configurable trough FreeNAS / TrueNAS GUI
  • Allows script placement on encrypted pool


Usage: [-h] [-q] [-v] [-d] [-m] [-t TIMEOUT] [-p POLL_TIME] [-i DRIVE]

Monitors drive I/O and forces HDD spindown after a given idle period.
Resistant to S.M.A.R.T. reads.

A drive is considered as idle and is spun down if there has been no I/O
operations on it for at least TIMEOUT seconds. I/O requests are detected
during intervals with a length of POLL_TIME seconds. Detected reads or
writes reset the drives timer back to TIMEOUT.

  -q           : Quiet mode. Outputs are suppressed if flag is present.
  -v           : Verbose mode. Prints additonal information during execution.
  -d           : Dry run. No actual spindown is performed.
  -m           : Manual mode. If this flag is set, the automatic drive detection
                 is disabled.
                 This inverts the -i switch which then needs to be used to supply
                 each drive to monitor. All other drives will be ignored.
  -t TIMEOUT   : Number of seconds to wait for I/O in total before considering
                 a drive as idle.
  -p POLL_TIME : Number of seconds to wait for I/O during a single iostat call.
  -i DRIVE     : In automatic drive detection mode (default): Ignores the given
                 drive and never issue a spindown command for it.
                 In manual mode [-m]: Only monitor the specified drives.
                 Multiple drives can be given by repeating the -i switch.
  -h           : Print this help message.

Deployment and configuration

The following steps describe how to configure FreeNAS / TrueNAS and setup the script.

Configure disk standby settings

To prevent the smartctl daemon or TrueNAS from interfering with spun down disks open the TrueNAS GUI and navigate to Storage > Disks.

For every disk that you would like to spin down click the Edit button. Then set the HDD Standby option to Always On and Advanced Power Management to level 128 or above.

HDD standby settings

Note: In older versions of TrueNAS/FreeNAS, it was required to set the S.M.A.R.T Power Mode to Standby. This setting was configured globally and was located under Services > S.M.A.R.T. > Configure.

Deploy script

Copy the script to your NAS and set the execute permission trough chmod +x

That's it! The script can now be run, i.e. in a tmux session. However, an automatic start during FreeNAS's boot sequence is highly recommended (see next section).

Automatic start at boot

There are multiple ways to enbale the spindown timer after startup. The easiest one probably is to register it as an Init Script within the FreeNAS GUI. This can be done by opening the GUI and navigating to Tasks > Init/Shutdown Scripts and creating a new Post Init task that executes after boot.

Spindown timer post init task

Note: Be sure to select Command as Type

Note: With FreeNAS-11.3 a Timeout was introduced. However, the spindown script is never terminated by FreeNAS, regardless of the configured value. Therefore, keep Timeout at the default value of 10 seconds for now.

Delayed start (i.e. script placed in encrypted pool)

If you've placed the script at a location that is not available right after boot a delayed start of the spindown timer is required. This for example applies to situations where the script is located inside an encrypted pool which needs to be unlocked prior to execution.

To automatically delay the start until the script file becomes available the helper script is provided. It takes the full path to the spindown timer script as it's first argument. Additional arguments are passed to the called script once available. Example usage: ./ /mnt/pool/ -t 3600 -p 600

The script however must again be placed in a location that is available right after boot. To circumvent this problem you can also use the following one-liner directly from an Init/Shutdown Script as shown in the screenshot below. Set SCRIPT to the path where the file is stored and configure all desired call arguments trough setting them in the ARGS variable. The CHECK variable determines the delay between execution attempts in seconds.

/bin/bash -c 'SCRIPT="/mnt/pool/"; ARGS="-t 3600 -p 600"; CHECK=60; while true; do if [ -f "${SCRIPT}" ]; then ${SCRIPT} ${ARGS}; break; else sleep ${CHECK}; fi; done'

Spindown timer delayed post init task

Note: Be sure to select Command as Type

Note: With FreeNAS-11.3 a Timeout was introduced. However, the spindown script is never terminated by FreeNAS, regardless of the configured value. Therefore, keep Timeout at the default value of 10 seconds for now.

Verify autostart

You can verify execution of the script either using a process manager like htop or simply by using the following command: ps -aux | grep ""

When using a delayed start keep in mind that it might take some seconds before the script availability is updated and the spindown timer is finally executed.

Verify drive spindown (optional)

It can be useful to check the current power state of a drive. This can be achieved using one of the following commands, depending on your device type.

ATA drives

The current power mode of an ATA drive can be checked using the command camcontrol epc $drive -c status -P, where $drive is the drive to check (e.g. ada0).

It should return Current power state: Standby_z(0x00) for a spun down drive.

SCSI drives

The current power mode of a SCSI drive can be checked trough reading the modepage 0x1a using the command camcontrol modepage $drive -m 0x1a, where $drive is the drive to check (e.g. da0).

A spun down drive should be in one of the standby states Standby_y or Standby_z.

A detailed description of the available SCSI modes can be found in /usr/share/misc/scsi_modes.

Advanced usage

In the following section advanced usage scenarios are described.

Automatic drive detection vs manual mode [-m]

In automatic mode (default) all drives of the system, excluding the ones specified using the -i switch, are monitored and spun down if idle.

In scenarios where only a small subset of all avaliable drives should be spun down one can explicitly use the manuel mode trough supplying the -m flag. This disables the automatic detection of all drives. Furthermore the -i switch is inverted in manual mode. It then can be used to list all drives that should explicitly get monitored and spun down when idle.

An example in which only the drives ada3 and ada6 are monitored would look like this:

./ -m -i ada3 -i ada6

It is also possible to run multiple instances of the script with independent TIMEOUT values for different drives. In the following example all drives expect ada0 and ada1 are spun down after being idle for 3600 seconds where ada0 and ada1 are already spun down after 600 seconds of being considered as idle:

./ -t 3600 -i ada0 -i ada1    # Automatic drive detection
./ -m -t 600 -i ada0 -i ada1  # Manual mode

To verify the correct drive selection, a list of all drives that are being monitored by the running script instance is printed directly after starting the script (except in quiet mode [-q]).


Heavily spinning disk drives up and down increases disk wear. Before deploying this script, consider carefully which of your drives are frequently accessed and should therefore not be aggressively spun down. A good rule of thumb is to keep disk spin-ups below 5 per 24 hours. You can keep an eye on your drives Load_Cycle_Count and Start_Stop_Count S.M.A.R.T values to monitor the number of performed spin-ups.

Please do not spin down your drives in an enterprise environment. Only consider using this technique with small NAS setups which idle most time of the day and select a timeout value appropriate to your usage behavior.

Another useful scenario i.e. is spinning down drives that are only used once a day (e.g. for mirroring of files or backups).

Bug reports and contributions

Bug report and contributions are welcome! Feel free to open a new issue or submit a merge request :)


The script is heavily inspired by:


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Monitors drive I/O and forces HDD spindown after a given idle period. Resistant to S.M.A.R.T. reads.




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