Is the Unified Buffer Cache (ubc) on by default
now with NetBSD 1.6?

When the UBC is enabled, what is the purpose
of the original file system buffer cache?
Is it only used to buffer file meta-data?
(in routines like vflushbuf() I notice a 
call to VOP_PUTPAGES() which flushes 
all VM data cache pages for the file,
and *then* calls to bwrite() --
this appears redundant).

Thanks for your help!
Dave F.