RAC Re: One of the ASM concepts isn't clear for me. Can anybody explain?
- From: "K Gopalakrishnan" <kaygopal@xxxxxxxxx>
- To: j.velikanovs@xxxxxxxxx
- Date: Thu, 29 Jun 2006 19:28:38 -0700
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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