Re: 64 node Oracle RAC Cluster (The reality of...)
- From: Mladen Gogala <gogala@xxxxxxxxxxxxx>
- To: Kevin Closson <kevinc@xxxxxxxxxxxxx>
- Date: Wed, 22 Jun 2005 04:16:56 +0000
On 06/21/2005 11:53:35 PM, Kevin Closson wrote:
> this is not true for a real CFS. A proxy-cfs or nfs
> exhibits the characteristics you fear, but not a
> fully symmetric, concurrent read:write CFS. Demand
> paging is nothing more than the internals of mmap
> which in turn is really nothing more than an IO.
> Oh, with one exception, it is entirely 100% read only
> (a major text fault that is). That concern is a
> red herring. Binaries execute just fine from a CFS.
Kevin, I heard your name before and I am fully aware that you know much more
then me. Truly symmetric clustered FS that I used to work with was known as
Files-11. DEC representative used to tell us, I quote, "not to do image
activation
from remote nodes". As you probably know, VMS did not do file caching before
version 6. The only question I have is synchronization of caches across the
nodes.
How can you achieve speed similar to the local FS? OS utilities usually do not
support direct I/O. Oracle released a plug-in replacement for Linux utilities,
so
that you have ftp, cp, dd, ls, tar and cpio being able to utilize direct I/O.
The
thing still doesn't work for scp and sftp. So, how do you get around
synchronizing
caches on different nodes? I assume that there is a concept similar to SCN which
gets increased with each transaction and if local SCN is higher then the global
one, then you know that there was a change on your side and send all buffers
with
the increased SCN to the other guy or write the blocks down to the disk and
have
the other nodes re-read them (OPS technique). It still looks like a significant
overhead which would slow down normal file operations significantly and make
things
like "vi $ORACLE_HOME/network/admin/listener.ora" fairly expensive. That would
also
interfere with the database operation and compete for the same bandwidth,
wouldn't it?
--
Mladen Gogala
Oracle DBA
--
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