I made a water simulation and cache to disk 150 frames (compress / cache to disk / unpack…)
Today I want to restart from 150 to 200.
How to do it?

Unfortunately, you would have had to enable save .SIM files. Then you could resume. If you don't have those, you'll have to simulate it all again.

« enable save .SIM files »?
What do you mean?

I prepared all my elements for the fluid animation, then I clicked « saved to disk ». 150 frames were calculated.
Next day I saw that I need around 50 more frames.

What/where is this things that you are talking about?

https://www.sidefx.com/forum/topic/96255/#post-423205 [www.sidefx.com]

tamte
https://www.sidefx.com/forum/topic/96255/#post-423205 [www.sidefx.com]

The document is a bit confusing to me... the .sim caching is only mentioned in DOP workflow section. What if I use SOP workflow? How could I save/resume a sim in this case?

You can unlock it and use the cache parameters on the DOPnet node inside, if not promoted

So you say that I have to put a checkpoint to the frame 150? Then I could resume and push it to 200?
Or it means this sim is lost, but for the future sim if I put regulary checkpoint I will be able to extend easely the anim?

That sim is lost unless you restart it. There usually is a lot more data saved in .sim files than in cache files destined for render, which would make writing them systematically very disk-space consuming. Hence why it's off by default, and why even if on, users will usually only save snapshots at larger frame intervals.