To solve this doubt, I decided to test the notebook Acer Aspire 4332, with processor Intel Celeron 900, 1 core; 2Gb DDR2 memory.
FatDog64 operating system, booted by the overlay mode created by Wiak.
First, with the system compressed into XZ, which is my usual mode, where the system has files SFS with a total size of 236Mb.
Booted in 42 seconds, with RAM usage between 152Mb and 168Mb. I installed Firefox and the size is busy in RAM it was 590Mb.
Running Firefox, watching a video on NETFLIX, RAM consumption was 909Mb and ZRAM was 98Mb.
Soon after, with the system compressed in ZSTD, the SFS file system got the size total at 296Mb.
Booted in 33 seconds, with RAM usage between 142Mb and 158Mb. I installed Firefox and the size is busy in RAM it stayed at 650Mb.
Running Firefox, watching the same video on NETFLIX, RAM consumption was 1Gb and ZRAM was 299Mb.
So, in my opinion, the gain of 9 seconds in initialization does not justify the use of ZSTD compression why do SFS files get bigger, take up more space in RAM and the consumption of RAM running applications as well got bigger.
1- This test is valid for the aforementioned notebook;
2- This test is useful for users who have a notebook with the same or similar configuration;
3- I also tested the GZIP format (similar results to ZSTD) and LZ4 (where the SFS files got much bigger) and the functioning of Firefox was hampered, with crashes.
4- The "bottleneck is the 2Gb memory. The 1 core Celeron, even from the service account ....
I hope this test is useful for some user of the forum, regardless of which system they use and, with other machines, other results!
Good luck to everyone!
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Mod edit: Change title to reflect the question better.