DB: 2 node RAC on ASM

Hi all,

I have to make a parameter change to increase the sga in our RAC db. I noticed that the system was using a pfile for each instance but seems like there is an SPFILE present there as well on the O/S pointing to an spfile in ASM.

SQL> select count(*) from v$spparameter where value is not null;

I have to increase the sga_target so do i need to (for each instance) :
1/ shutdown the instance
2/ modify sga_target in the pfile
3/ startup

The above should work? However I am unsure why the spfile is not working properly (or not being used). If i do:

SQL> create pfile='/home/oracle/init.ora' from spfile;
create pfile='/home/oracle/init.ora' from spfile
ERROR at line 1:
ORA-27046: file size is not a multiple of logical block size
Additional information: 1
The above is probably because the spfile is in ASM. There is an spfile on the O/S for each node, when i do:

[oracle@mgdb2 dbs]$ strings spfilebof21.ora
I am a bit confused on how the spfile works with RAC, i understand it is placed in the ASM so all instances can access it.

Thanks in advance!