Thanks, Bret. I will check your doc carefully. I ask this question is because of following I don't understand:
1. in mydb, there is a default segment system. it across 2 devices: the info from sp_helpsegment 'system' is:
device size free_pages
dev1 2000.0MB 491760
dev2 4000.0MB 264
but when I check the space with DBArtisan, see the screenshot:
less than 150M data total. 97% marked as other. but on dev2, only 264 free pages . That's why I'm confused. That's why I want to know what's data stored on dev2. As developer tell me, dev2 should not have much data on it.