Thanks @nebulon for your time, together with ChatGPT I did deeper analysis but I also read this: https://docs.cloudron.io/troubleshooting/#mysql
Two instances of MySQL
There are two instances of MySQL on Cloudron. One instance runs on the host and is used by the platform. Another instance is the MySQL addon which runs in a container named mysql and is shared by apps. This test is related to the host MySQL.
Doesn't this mean that the mysql service in iotop is the "host version" that has nothing to do with the apps?
For now "we" (I) have seen this:
Summary of Disk Write I/O Observation on Cloudron Host
Using iotop, the host shows consistently high disk write I/O (4–5 MB/s).
Analysis of MySQL processes (mysqld) indicates these are responsible for the majority of the write load.
The high write I/O is primarily due to InnoDB internal activity: buffer pool flushes, redo log writes, and metadata updates, mostly from the box database (eventlog, tasks, backups).
In about 10 minutes this is the Disk Write I/O (so 1.5GB in 10 minutes)
Total DISK READ: 0.00 B/s | Total DISK WRITE: 2.73 M/s
Current DISK READ: 0.00 B/s | Current DISK WRITE: 4.25 M/s
TID PRIO USER DISK READ DISK WRITE> SWAPIN IO COMMAND
21250 be/4 messageb 0.00 B 1038.50 M ?unavailable? mysqld
936 be/4 mysql 0.00 B 465.28 M ?unavailable? mysqld
I stopped about 25% of the apps at a certain moment with no significant result, this is the current situation (IMHO not really intensive application and they have low traffic):
App Status
Yourls Running
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Stopped
WordPress (Developer) Running
WordPress (Developer) Stopped
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Running
WordPress (Developer) Stopped
WordPress (Developer) Running
Taiga Stopped
Surfer Running
Surfer Stopped
Roundcube Running
Roundcube Running
Omeka S Stopped
Moodle Stopped
LAMP Running
Roundcube Running
Roundcube Running
Roundcube Running
Pretix Stopped
MiroTalk SFU Running
Matomo Running
FreeScout Running
FreeScout Running
Espo CRM Running
What to do next to find the root cause?