IDS 10 erratic run times

IDS 10.0FC3 on Solaris 2.9 This is a brand new server which we are preparing to migrate a v9 system to. Over the past few weeks I have run multiple dbimports from more-or-less the same data source - certainly the same schema - but the import time varies widely. The fastest I've done it is 9h, the slowest 14. This weekend's took 13h 10m. There's never anyhting else going on on it. In the UPDATE STATISICS phase the elapsed time was 3h: during the "fast" run it was just 1h. I had a look during this period: often onstat -p onstat -m onstat -D would show periods of perhaps 2 minutes with no activity at all: no bufreads or physreads, no checkpointing for 20 minutes (the checkpoint interval is 5 mins), the relevant thread just "sleeping forever". I haven't changed the disk layout (a 60G database striped across three disks in a JBOD array with the standard Solaris LVM interlace of 16k, this stripe mirrored to another 3 disks identically configured attached to another controller on the same array); I have experimented with different buffer sizes (perversely one 9h run was with BUFFERS set to just 100,000 rather than the usual 1,000,000 although there's no consistent pattern to this now I've cut the LRU MIN and MAX, and I've had another 9h run with the 2GBytes of BUFFERS since). It's the fact that all activity just seems to stop for long periods that puzzles me. If, during such a period, I fire up dbaccess and run a sysmater query it returns instantly, so I can't see a systemic cause. The new box is still 1.5 to twice the speed of the old in comparative testing but this disparity in times is just puzzling me and I don't want it to come back and bite us after go live. Any suggestions or inspiration welcome! thanks Neil