One of the ASM concepts isn't clear for me. Can anybody explain?

Hello community,

Just wonder if anybody from you can comment:

A.FS
In case of a regular File System (FS) Oracle process passes file name and relative block number to FS/OS code is responsible for retrieving the particular block to the process, right?

B. RAW
In case of raw device Oracle process opens device and requests device driver to retrieve the particular block by providing offset of it.

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?

PS Never worked with ASM so far. Pointers to the documentation there this question would be covered really appreciated.

Thank you in advance,

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Yury
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