Re: ASM and RAID
From: Michael Austin <maustin_at_firstdbasource.com>
Date: Mon, 19 Jan 2009 21:09:06 -0600
Message-ID: <qfbdl.11683$as4.5742_at_nlpi069.nbdc.sbc.com>
Robert Klemme wrote:
> On 18.12.2008 17:32, Michael Austin wrote:
>
> That's an interesting bit of information. How is the ASM able to
> replace a clustered file system? Does it provide only the meta data
> layer which controls concurrent access to files?
>
> I am assuming you mean this one: http://www.amazon.com/dp/0071496076
Date: Mon, 19 Jan 2009 21:09:06 -0600
Message-ID: <qfbdl.11683$as4.5742_at_nlpi069.nbdc.sbc.com>
Robert Klemme wrote:
> On 18.12.2008 17:32, Michael Austin wrote:
>> ASM also does not do the actual reading/writing - the RDBMS does. In >> other words - ASM does not proxy the I/O for the RDBMS - RDBMS writes >> directly to the data files. ASM just tells the RDBMS what the extent >> map is and only at file open time... which is why you need additional >> shared_pool (1MB for every 100GB of file space).
>
> That's an interesting bit of information. How is the ASM able to
> replace a clustered file system? Does it provide only the meta data
> layer which controls concurrent access to files?
Sorry taking so long to get back to this thread...
In order to have a "clustered file system" one of the prerequisites is to have some method of I/O fencing - a mechanism to prevent both servers from writing the same data block at the same time. This is what Cache Fusion which includes the Distributed Lock Manager (DLM) is for - to allow concurrent writes to raw devices from multiple servers in a RAC cluster.
If you ever worked in an OpenVMS environment - this is how they made it work... The DLM is the most important piece of this whole thing. Without it, you would have chaos.
>
>> There is a book called Automatic Storage Management - practical >> under-the-hood ??? that is very good at the mechanisms within ASM and >> RDBMS...
>
> I am assuming you mean this one: http://www.amazon.com/dp/0071496076
Yes.
>
> Kind regards
>
> robert
Received on Mon Jan 19 2009 - 21:09:06 CST