ASM AMM questions

Question

Hi,
I now have the strangest behaviour here. That is, it puzzles me.
I have an Oracle 11.1.0.7 ASM single instance on an IBM AIX 5.3 TL 06 server
There is no database configured yet to use this ASM instance as storage.
What I see here is that any setting of SGA_MAX_SIZE less than 90M results in an error. SGA_MAX_SIZE of 90M is the absolute minimum on this server.
Now the "problem":
On normal - i.e. non-ASM - instances as far as I know sga_max_size is the absolute maximum whereas sga_target can be tuned up to this size
On my ASM instance whenever I only set sga_max_size=90M the instance starts up as expected:
SQL> startup nomount
ASM instance started
Total System Global Area *96026624* bytes
Fixed Size 2151248 bytes
Variable Size 68709552 bytes
ASM Cache 25165824 bytes
SQL>
Now when I set SGA_TARGET also to the same value something strange happens.
First only in memory:
SQL> alter system set sga_target=90M scope=memory;
System altered.
SQL> show sga
Total System Global Area *96026624* bytes
Fixed Size 2151248 bytes
Variable Size 68709552 bytes
ASM Cache 25165824 bytes
SQL>
Seems OK, doesn't it ?
Now in the SPFILE:
SQL> alter system set sga_target=90M scope=spfile;
System altered.
SQL> shutdown immediate
ORA-15100: invalid or missing diskgroup name
ASM instance shutdown
SQL> startup nomount;
ASM instance started
Total System Global Area 162856960 bytes
Fixed Size 2151848 bytes
Variable Size 135539288 bytes
ASM Cache 25165824 bytes
Now why has the total SGA size increased to 156M.
It's even more strange when I remove the SGA_MAX_SIZE from the spfile and only set SGA_TARGET=90M. Then
SQL> startup nomount;
ASM instance started
Total System Global Area 283930624 bytes
Fixed Size 2153056 bytes
Variable Size 256611744 bytes
ASM Cache 25165824 bytes
SQL>
Please note: Removing sga_max_size from the spfile is done by recreating it from an pfile
Anyone a suggestion in how to set the AMM parameters for an ASM instance so it behaves like expected, or at least like a "normal" database?
Thanks

Answer 1

The answer is quite simple - ASM currently does not employ the Oracle Database 10g Automatic Memory Management feature. There was significant optimizations done in 11gR1 with respect to memory management, thus there is no
need to set the SGA parameters in 11gR1. ASM now leverages the MEMORY_TARGET parameter and
the default of 256MB is more than enough for the ASM instance. The management of (ASM) processes
was also optimized, therefore the processes parameter also does not need to be set in 11gR1.
You can reffer to metalink note 265633.1 - there is a pdf document and that describes what should be set and what is not supported.
ASM is not a "normal" database.
Edited by: Laura Gaigala on May 6, 2009 4:27 PM