Also, I wouldn’t shy from keeping the database on the same, fast storage as the OS, even if that’s flash. Move to an external SSD when you can. HDDs have such long seek times.

Very much true. I installed Immich on my dads Synology for him and compared to my own setup at home the speeds are abysmall (it even crased a few times during the first indexing and ML run). I suspect a major part is that the whole os runs on an hdd.

If you put the database on an sd-card just ensure you make frequent backups somwhere else. I wouldn’t trust flash storage to keep my data safe.