Checkpoint takes long

Hi, on our SCO 5.0.4 machine we are running ODS 7.20 UC3. During the day when appr. 60-80 persons are using the machine, we permanently experience checkpoints that take 10 seconds or longer. I tried changing the time between checkpoints from 1 minute to 10 minutes and back to the default of 5 minutes, the checkpoints will always take very long. We have set the physical log size to 20000 and use 30 logical logs, each 2048. Our buffers are set to 100000, LOCKS 300000, LRU_MAX_DIRTY 2, LRU_MIN_DIRTY 0, LRUS 12.Which parameters affect the checkpoint time mostly? Thanks and regards, Kai