Questions on INDEX(ES), TEMP DBSPACES and ONCHECK(S)

Hi everybody. Some very general questions on the above topics ( not necessarily related ) TEMPDBS: 1. what is the difference between having multiple dbspaces ( on different disks ) and having multiple chunks ( on different disks ) on one huge temp dbspace ?? Is there a performance issue ? 2. How would I know if the size ( configuration ) of my temp dbspace is causing a performance bottleneck ?? INDEXES: 1. Does informix re-build the index everytime a modification happens to the table ? Or does this depend on the type of index ? I assume that is does, though I have been answered to the contrary. 2. What is the need to re-build an index on a table and how often should we do it ? Is re-building required to organise the index extents ?? What is meant by an index being "out of date" ? ONCHECKS: 1. How often should one oncheck ? 2. Is it recommended to do an oncheck -p BEFORE an oncheck -c ? Why ? 3. How do I speed up the performance of an oncheck ( specially the table and index checks ? ) and what does the performance depend upon I realise that this is too many question in one mail. It doesn't matter if you don't have an answer/opinion on all of them, please reply anyway. Thanks as always Sujata