Strange freezes in Debian Buster on an i5

Hello,
a few weeks ago I started to experience strange things on my Dell Vostro i5.
The laptop has 8Gb ram, a 120Gb SSD and it is running Debian Buster (upgraded from Debian Stretch).

What happens is this, at intervals, the computer becomes unresponsive with the HDD led on.
I tried to debug this with htop, but to no avail as everything freezes for several seconds.
After around 10 seconds, the HDD led goes off and the laptop is responsive again.

I have installed earlyOOM to see if it was a memory leak issue, but it did not help.
What would be the best way to monitor this and identify the culprit?
It seem to happen more frequently when firefox is open, but not always.

Any suggestion please?

Originally Posted by assasukasse What happens is this, at intervals, the computer becomes unresponsive with the HDD led on. I tried to debug this with htop, but to no avail as everything freezes for several seconds. After around 10 seconds, the HDD led goes off and the laptop is responsive again.

Let's assume that something uses the HDD so much that it blocks the system. This is possible.
Please search for it in the logs.
BTW, is HDD a secondary drive, SSD being the primary that the system is installed to?

Thanks for the answer,
Could you please put me in the right direction to which logs should I look at?
The system has only one drive, SSD Cruzer with btrfs on it and subvolumes. It also has 8Gb swap on it.

I experience sometimes the same type of freeze (dell precision debian bullseye 12Gb 2 HDD ) I have not investigated further but I have noticed that this happens (always ?) when I have thunderbird and libreoffice opened with numerous files at the same time. In case it helps...

Have a look with iotop and/or fatrace. The latter will generate a ton of output - you never knew how much I/O was going on in your system. Write it to a file and condense it with your favourite tool - awk, perl, python ... whatever