No you don’t have to turn flashback database on to use a data guarded snapshot standby… but does it still use flashback logs?
Yes by default when you convert a physical standby to a snapshot standby, flashback is turned on automatically. Flashback will be OMF based and Oracle puts flashback logs in the FRA, and then a guaranteed restore point is created.
What if you have no FRA? Good question. An FRA is required to use snapshot standbys at least on the standby.
If for some reason you don’t use an FRA on the primary, like many shops that use MML (Media Management Layer API e.g. backup to Netbackup, Tivoli etc.) based RMAN then you are probably still good.
As long as you never switchover and try to use a snapshot standby in a place where an FRA does not exist you will be fine.
Here’s SQL / a query that shows you where the flashback logs are created (only returns rows when in “snapshot standby”, physical standbys return 0 rows:
SQL> l 1 SELECT 2 log# as "Log No", 3 thread# as "Thread No", 4 sequence# as "Seq No", 5 name, 6 bytes/1024/1024/1024 as "Size(GB)", 7 first_change# as "First Chg No", 8 first_time 9 FROM 10 v$flashback_database_logfile 11* ORDER BY first_time SQL> / 2 1 2 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 11,494,212 22 SEP 2017 13:46:06 k/o1_mf_dwblx63f_.flb 3 1 3 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 11,494,312 22 SEP 2017 13:46:08 k/o1_mf_dwbm3033_.flb 4 1 4 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 11,494,413 22 SEP 2017 13:46:14 k/o1_mf_dwbm30kn_.flb 5 1 5 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 11,494,525 22 SEP 2017 13:46:21 k/o1_mf_dwbm3717_.flb 6 1 6 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 11,494,623 22 SEP 2017 13:46:28 k/o1_mf_dwbm3fg1_.flb 7 1 7 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 11,494,723 22 SEP 2017 13:46:33 k/o1_mf_dwbm3pyf_.flb 8 1 8 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 11,494,830 22 SEP 2017 13:46:41 k/o1_mf_dwbm3tdj_.flb 9 1 1 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 0 k/o1_mf_dwbm43t4_.flb 1 1 1 /u01/app/oracle/fast_recovery_area/GGSTBY/flashbac 0 0 k/o1_mf_dwblx4s1_.flb 9 rows selected. SQL>