Q1. What is the difference between an ASM Disk Group and an ADVM Volume ?
To my mind, an ASM Disk Group is effectively a logical volume for Database files ( including FRA files ).
11gR2 seems to have introduced the concepts of ADVM volumes and ACFS File Systems.
An 11gR2 ASM Disk Group can contain :
- ASM Disks
- ADVM volumes
- ACFS file systems
Q2. ADVM volumes appear to be dynamic volumes.
However is this therefore not effectively layering a logical volume ( the ADVM volume ) beneath an ASM Disk Group ( conceptually a logical volume as well ) ?
Worse still if you have left ASM Disk Group Redundancy to the hardware RAID / SAN level ( as Oracle recommend ), you could effectively have 3 layers of logical disk ? ( ASM on top of ADVM on top of RAID/SAN ) ?
Q3. if it is 2 layers of logical disk ( i.e. ASM on top of ADVM ), what makes this better than 2 layers using a 3rd party volume manager ( eg ASM on top of 3rd party LVM ) - something Oracle encourages against ?
Q4. ACFS File systems, seem to be clustered file systems for non database files including ORACLE_HOMEs, application exe's etc ( but NOT GRID_HOME, OS root, OCR's or Voting disks )
Can you create / modify ACFS file systems using ASM.
The oracle toplogy diagram for ASM in the 11gR2 ASM Admin guide, shows ACFS as part of ASM. I am not sure from this if ACFS is part of ASM or ASM sits on top of ACFS ?
Q5. Connected to Q4. there seems to be a number of different ways, ACFS file systems can be created ? Which of the below are valid methods ?
- through ASM ?
- through native OS file system creation ?
- through OEM ?
- through acfsutil ?
my head is exploding
Any help and clarification greatly appreciated
Jim