Re: 64 node Oracle RAC Cluster (The reality of...)

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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