If OSTs are permanently deactivated via lctl conf_param <fsname>.OSTnnnn.active=0 they still appear in the lfs df output, which can be annoying to users.
UUID 1K-blocks Used Available Use% Mounted on
myth-MDT0000_UUID 9174328 1213448 7436592 14% /myth[MDT:0]
myth-OST0000_UUID 3880285544 3528483608 157762960 96% /myth[OST:0]
myth-OST0001_UUID 3886052008 3412584200 279155192 92% /myth[OST:1]
myth-OST0002_UUID 3880285544 3555131444 208731780 94% /myth[OST:2]
myth-OST0003_UUID 5840741952 4523261952 1025405712 82% /myth[OST:3]
OST0004 : inactive device
filesystem summary: 17487365048 15019461204 1671055644 90% /myth
If the OST is permanently deactivated (as opposed to disconnected or otherwise unavailable due to error) don't list the OST in lfs df unless -v is also given. That will remove this annoying output from normal usage, but still allow the full OST listing to be generated if needed for some reason.