Non-geeks may want to look away now.
It never fails to amaze me that otherwise bright people seem to think that just using RAID or a SAN is sufficient to spread data around.
Informix was completely rebuilt to make best use of SMP technology, which means that it likes to parallelize tasks where it possibly can.
But Informix cannot be made aware of operating system-level data distribution. If you want to use things like fragment elimination, PDQ, etc., then you have to use Informix's fragmentation. (You can, of course, use this on top of RAID / SAN / whatever.) But if you just use the storage subsystem to partition or fragment the data, then as far as Informix is concerned, it's all in one big pot.
This can not only make all the desirable parallelisation options unavailable, but can also lead to disk contention, long checkpoints, teenage pregnancies and athlete's foot.
I'll post some ruminations on actual fragmentation strategies in the future.
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