Configure btrfs-balance to run out of production times

In general a btrfs balance may have an impact on the systems performance, especially on busy ones.
To avoid a balance run during production times systemd offers some very flexible tools to re-schedule the service.

SLES12 SP5 requires a different solution since the btrfsmaintenance tools utilize cron. 
 

SLES15 SP3 and later:
To avoid btrfs balance running during production times lets
define a window of 24 hours on Sundays.

Step 1:

sles15sp62:~ # vi /etc/sysconfig/btrfsmaintenance

and change

BTRFS_BALANCE_PERIOD="weekly"

to

BTRFS_BALANCE_PERIOD="Sun *-*-* 00:00:00"

Due to this change, the balance now will always start on Sundays at 00:00 AM. However, it may not be desired to have all systems in a particular environment start at the same time, therefore a random delay is required for the job:

sles15sp62:~ # systemctl edit btrfs-balance.timer

add

[Timer]
RandomizedDelaySec=86400

The value 86400 has been chosen in this example because a day has 86400 secs, so the job can run on any time at Sundays. Feel free to adjust as applicable. 
After editing and saving the file, success of the operation is shown as:

Successfully installed edited file '/etc/systemd/system/btrfs-balance.timer.d/override.conf'.

As a last step, reload the changed settings:

systemctl daemon-reload

systemd is able to show when a job will be run:

sles15sp62:~ # systemctl status btrfs-balance.timer
● btrfs-balance.timer - Balance block groups on a btrfs filesystem
     Loaded: loaded (/usr/lib/systemd/system/btrfs-balance.timer; enabled; preset: enabled)
    Drop-In: /etc/systemd/system/btrfs-balance.timer.d
             └─override.conf, schedule.conf
     Active: active (waiting) since Thu 2024-09-26 10:13:41 CEST; 2min 0s ago
    Trigger: Sun 2024-09-29 11:42:02 CEST; 3 days left
   Triggers: ● btrfs-balance.service
       Docs: man:btrfs-balance

As already noted SLES12 SP5 works in a different way:

sles12sp51:~ # vi /etc/sysconfig/btrfsmaintenance

change

BTRFS_BALANCE_PERIOD="weekly"

to

BTRFS_BALANCE_PERIOD="none"

Now create a cron job for the btrfs-balance job

sles12sp51:~ # sudo su
sles12sp51:~ # crontab -e

and add

RANDOM_DELAY=660
0 0  * * SUN  /usr/share/btrfsmaintenance/btrfs-balance.sh

crontab: installing new crontab

Note:
The behaviour of the variable RANDOM_DELAY in crontabs is described in "man 5 crontab".
Please note: In opposite to RandomizedDelaySec, the unit of the variable RANDOM_DELAY is given in minutes.