Thank you Gopal,
It makes sense. Looks like in an ASM configuration Oracle Instance have got additional functions that in FS cse is FS/OS responsibility area. Before your explanation I thought that ASM is taking care of almost all. Now it sounds like ASM & Oracle DB Instances sharing functionality that previously have been dedicated to FS.
Thank you again for your explanation, Yury
> C. ASM Question !!!! > > Question is that is going on in case of ASM? > Oracle instance doesn't pass an IO request to ASM. It is clear. ASM is > there just for providing metadata for all Oracle instance about files' > blocks location/offset. > Does Oracle Instance asks ASM about offset of the particular block the > Instance is interested in each time it needs issue IO request or each > Oracle instance has additional data structures (cache) to stores > metadata about offsets and physical layout of the particular disc > group and files located on it?
During startup (when you use ASM for storage), the database instance communicates with ASM instance and gets the extent map from ASM and caches the extent map in database instance's cache. From now onwards we use the extent map cached in the database instance.
We do not go to ASM instance for every IO request. We go to ASM instance only when there is a change in the extent map (due to rebalancing or adding/removing disk groups)
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