Re: Optimising IDS for RAID-5 ?

Andrew Lawrenson wrote: > > Does anyone have any clues as to how to best tune Informix (v7, currently > 7.23) to run on RAID-5, in terms of LRU's, CLEANERS, LRU_MIN/MAX_DIRTY, Read > Ahead, etc? I my case, this is all under NT 4.0 Tuning these things is very dependent on your goals for the server, service requirements, what else is sharing the machine, specific load mix (reads -vs- writes). In general, more LRUS better than fewer to support more concurrent buffer requests, but if you have few uses you can do away with the overhead. Considering you will not have much memory for lots of BUFFERS, try 17 LRUS (avoid 16,64,&96 LRUS). CLEANERS >= LRUS to minimize checkpoint times but if you are read intensive and updates pausing several seconds for checkpoints will not cause your users any grief you can again reduce overhead by reducing CLEANERS. Similarly LRU_MAX/MIN_DIRTY will affect checkpoint times and the interaction of Informix with other processes. If the system is dedicated to Informix then minimize LRU_MIN/MAX_DIRTY toward 0 & 1 to minimize the checkpoint times and spread I/O over the time between checkpoints. If not dedicated this may slow I/O for other processes. ReadAhead depends on two things, the nature of the data queries and index structure and the relative speed of the disk farm -vs- CPU. With PC non-caching controllers and a single controller path the read ahead will probably need to be large with as much as 50% of the RA_PAGES value for the RA_THRESHOLD. If you do a lot of sequential scans or your index pages are contiguous (as they will be if built onto static tables after data is loaded or if the index is detached) then you can usually take better advantage of ReadAhead. Try starting with 64 & 16, this is a typical set of values for a PC based system, more if the CPU is better than a P300. Art S. Kagel