Re: ASM tracking datafiles

From: Dan Norris <>
Date: Wed, 25 Feb 2009 08:30:16 -0600
Message-ID: <>

> But ASM itself doesn't "care" about files as far as I've seen so far.

I don't think that's completely accurate. ASM has to care because it is the only one that (at least initially) knows where to find the files that the database needs. That's what V$ASM_FILE shows (in an ASM instance). I'm not sure where/how ASM relates each of the files in that view to databases--maybe it doesn't care about databases?

Once the extent map for a file is given to the RDBMS instance, the ASM instance isn't in the I/O path (it's built in to the RDBMS kernel). However, the initial request to open a file is looked up by the ASM instance and the extent map given to the RDBMS instance so that the RDBMS can open the file. So, I think Niall is right that ASM doesn't necessarily know which datafiles belong to which RDBMS, but when a request for a specific file is made from RDBMS to ASM, it is up to ASM to locate the file and all its parts and tell the RDBMS where to go to open the file it requested.

The information shown in V$ASM_FILE has to be stored in the ASM metadata on the ASM disks in the diskgroup where the file resides.


Received on Wed Feb 25 2009 - 08:30:16 CST

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