Date: Thu, 15 Mar 2012 21:17:45 +0100
the best source I have found:
Oracle Automatic Storage Management: Under-the-Hood & Practical Deployment Guide
When an RDBMS instance needs to open an ASM file, it sends to the ASM instance a file-open request, with the filename, via one of the o0nn processes. ASM consults the File Directory to get the extent map for the file. ASM sends the extent map to the RDBMS instance. In Oracle Database 10g, for datafiles, ASM sends the entire extent map to the RDBMS instance at file-open time. In Oracle Database 11g, for datafiles, ASM initially sends the 60 direct extents to the RDBMS instance. For the remaining extents, which are located in indirect extents, the RDBMS requests subsequent extent map sections on demand. ASM delivers all the extent map pointers in the same indirect extent as the requested file extent.
does this answer your question?
On Thu, Mar 15, 2012 at 19:03, Paul Harrison <cure_at_austin.rr.com> wrote:
> Hi All,
> RAC.. In database instance... I query for some data and the database
> instance has to communicate with the asm instance in order to get the path
> to the block within the asm disk group. Does the asm instance return all the
> pointers to the blocks one time(one round trip) or round trip per block?