There's an interesting thread on linux-kernel right now about O_DIRECT and the
kernel i/o APIs databases need. I noticed a connection between what they were
discussing and the earlier discussions here and the pining for an interface to
avoid having vacuum preempt other disk i/o.
Someone from Oracle is on there explaining what Oracle's needs are. Perhaps
someone more knowledgable than myself could explain what would most help
postgres in this area.
There was another thread I commented on that touched on another postgres
wishlist item. A way to sync IDE disks reliably without disabling write
caching entirely. There was some inkling that newer drives might provide for
such a possibility. Perhaps that too could be worth advocating for on
postgres's behalf.