HELP: Chunks turned 'offline' for no apparent reason! Reason?

Fellow Informix`ers, We have a problem that occurs quite often (about 50% of our customers). Every now and then, various chunks get turned 'offline' by the Online Engine. We have no way to turn them back on. An Informix engineer dials in, and turns the chunk back on-line using their astools (which they have not given us). Once the chunk is back online, and the database back up, we experience all sort of search problems via indexes. Simply dropping and recereating the indexes does nor fix the problem. We then have to export and reimport tables to get around. Every Informix engineer that dialed in, gave us a different reason for the chunk going offline. The reasons vary from disk problems (which AIX has not complained about), to a bug in ver 5.0 for AIX. Has anyone out there experienced this problem? Does anyone know of a better workaround than exporting and reimporting the tables? Any and all responses on this matter appreciated. Thanx, Raj.