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

On 6/30/06, K Gopalakrishnan <kaygopal@(protected):
>
>
> > 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?
>
>
> Yury:
>
>
> 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)
>
> -Gopal
>
>


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Yury
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