Introduction

On alpine Linux, there in no cron/script provided to scrub (and eventually trim) your pool(s) on a regular basis, like in other Linux distributions.
Setting it up is easy and can be done in a few minutes.

Scrub

Definition

The scrub examines all data in the specified pools to verify that it checksums correctly. For replicated (mirror, raidz, or draid) devices, ZFS automatically repairs any damage discovered during the scrub
When scrubbing a pool with encrypted filesystems the keys do not need to be loaded. However, if the keys are not loaded and an unrepairable checksum error is detected the file name cannot be included in the zpool status -v verbose error report.
A scrub is split into two parts: metadata scanning and block scrubbing. The metadata scanning sorts blocks into large sequential ranges which can then be read much more efficiently from disk when issuing the scrub I/O.

Also see Oracle - Disk Scrub - Why and When?

Creating the script

This script is used to list the pools, make sure they are online, and no scrub is being done at the time.
We will write it in /usr/libexec/zfs/scrub
It's taken from debian zfs scripts

Contents of /usr/libexec/zfs/scrub

Then make the script executable

# chmod +x /usr/libexec/zfs/scrub

Launching the scrub script with cron

It is recommended to launch a scrub regularly to assure your pool(s) and datas are in good shape.
Here, the scrub will be launched once a month, on the 2nd sunday of the month.

In root, edit your crontabs

# crontab -e

and add these 2 lines

# zfs scrub the second sunday of every month
24      0       8-14    *       *       if [ $(date +\%w) -eq 0 ] && [ -x /usr/libexec/zfs/scrub ]; then /usr/libexec/zfs/scrub; fi

Finally, make sure cron is launched:

# rc-update

There should be a line saying

crond |      default

If not, add it to the boot sequence

# rc-update add crond

then start the crond daemon

# rc-service crond start

Trim

Definition

Initiates an immediate on-demand TRIM operation for all of the free space in a pool. This operation informs the underlying storage devices of all blocks in the pool which are no longer allocated and allows thinly provisioned devices to reclaim the space.
A manual on-demand TRIM operation can be initiated irrespective of the autotrim pool property setting. See the documentation for the autotrim property above for the types of vdev devices which can be trimmed.

Creating the script

This script is used to list the pools, make sure they are online, build only with NVME ssd drive(s) and no trim is being done at the time.
We will write it in /usr/libexec/zfs/trim
It's taken from debian zfs scripts

Contents of /usr/libexec/zfs/trim

Then make the script executable

# chmod +x /usr/libexec/zfs/trim

Launching the scrub script with cron

Here, the scrub will be launched once a month, on the 1st sunday of the month.

In root, edit your crontabs

# crontab -e

and add these 2 lines

# zfs trim the first sunday of every month
24      0       1-7    *       *       if [ $(date +\%w) -eq 0 ] && [ -x /usr/libexec/zfs/trim ]; then /usr/libexec/zfs/trim; fi

Finally, make sure cron is launched:

# rc-update

There should be a line saying

crond |      default

If not, add it to the boot sequence

# rc-update add crond

then start the crond daemon

# rc-service crond start