I could see the following messages in Alertlog , was curious to know the reason behind it…
Mon Oct 10 11:49:00 2011
SUCCESS: diskgroup ARCH_QA was mounted
SUCCESS: diskgroup ARCH_QA was dismounted
SUCCESS: diskgroup ARCH_QA was mounted
SUCCESS: diskgroup ARCH_QA was dismounted
Mon Oct 10 11:50:00 2011
SUCCESS: diskgroup ARCH_QA was mounted
SUCCESS: diskgroup ARCH_QA was dismounted
SUCCESS: diskgroup ARCH_QA was mounted
SUCCESS: diskgroup ARCH_QA was dismounted
Mon Oct 10 11:51:00 2011
SUCCESS: diskgroup ARCH_QA was mounted
SUCCESS: diskgroup ARCH_QA was dismounted
SUCCESS: diskgroup ARCH_QA was mounted
SUCCESS: diskgroup ARCH_QA was dismounted
This is expected behavior. The messages you see are not errors (that is why they are prefixed with "SUCCESS"). The database instance is creating and then closing archive logs one at a time in the ARCH_QA disk group. Whenever a database closes its last file in a disk group, it dismounts the disk group. Whenever a database accesses a disk group when it does not have any other files open in the disk group, it mounts the disk group.
If you do not want to see the log messages frequently, you can put a mirrored control-file, or mirrored online redo, or dummy online tablespace data file on the diskgroup. This message will not be output frequently in this case. Because CKPT keeps opening a control-file, LGWR keeps opening an online redo, DBW keeps opening an online tablespace data file. So, the diskgroup is not dismounted until the database shutdown.
TailPiece: we get this messages only for respective ASM disk groups for archive logs are written and in a high number
Ref: Why FRA Diskgroup Gets Mounted/Dismounted ? [ID 603204.1]
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