ORA-00821 Specified value of sga_target is too small, needs to be at least

Resized your SGA_TARGET too small and found you can’t now start your database.

If you are using a PFILE then just edit it and set the SGA_TARGET to a larger value. But what if you’re using an SPFILE. One possibility is to create the pfile from the spfile edit the pfile, and then either start the database using the pfile and remove the spfile and start the database as normal and the new pfile will be picked up.

The problem arises when the spfile is in an ASM, creating the pfile from this can be a problem. One solution is to create a pfile which calls the spfile in the ASM but after the call to the spfile add an extra line which alters the SGA_TARGET as follows

SPFILE='+DATA1/PROD1/spfilePROD1.ora'
SGA_TARGET=1024M

This pfile can be places in $OH/dbs thus, the next time you start the database this pfile will be run. Alternatively, you could explicitly use the ‘pfile=’ parameter when starting the database thus

Startup pfile=$OH/dbs/initPROD1.ora