Newbee with questions about physical and logical log allocations.

Does anybody have a good rule-of-thumb calculating the size of the physical and logical log sizes. Informix said the total physical and logical logs size should be 20% of the total dbspace dedicated to online. Informix also indicates that the ratio of logical to physical logs size should be 3 to 1. What informix does tell you is how to arrive at the number of LOGFILES to be managed by informix. I know informix needs at least 3 logicals logs to perform log rotation, so if LOGFILES is set to 10 does informix attempt to allocate 10 logfiles of X LOGSIZE in side the root dbspace or does it allocate them dynamically when needed. I need this info to get a handle on how much raw disk space to dedicate to the root dbspace.