I upgraded my EX2300-24P and got an alarm light on the front.

root@switch> show system alarms
1 alarms currently active
Alarm time Class Description
2021-06-19 04:20:46 EDT Minor RE 0 /var partition usage is high

Then I ran “show system storage”

root@switch> show system storage
fpc0:
--------------------------------------------------------------------------
Filesystem Size Used Avail Capacity Mounted on
/dev/gpt/junos 1.3G 925M 331M 74% /.mount
tmpfs 756M 88K 756M 0% /.mount/tmp
tmpfs 324M 484K 324M 0% /.mount/mfs

I did some research and contacted Juniper. It appears that older version of Junos does not completely remove the older version when upgrading, and takes up disk space. To correct that issue

root@switch> start shell% pkg setop rm previous
% pkg delete old

To verify –

% cliroot@switch> show system alarms 
No alarms currently active

root@switch> show system storage 
fpc0:
--------------------------------------------------------------------------
Filesystem Size Used Avail Capacity Mounted on
/dev/gpt/junos 1.3G 507M 750M 40% /.mount
tmpfs 749M 88K 749M 0% /.mount/tmp
tmpfs 324M 484K 324M 0% /.mount/mfs