Because ASM files are Oracle-Managed Files (OMF), you don??™t need to specify any other
characteristics when you create the tablespace.
Disk Group Fast Mirror Resync
Mirroring the files in your disk groups improves performance and availability; when a failed disk
in a disk group is repaired and brought back online, however, the re-mirroring of the entire new
disk can be time consuming. There are occasions when a disk in a disk group needs be brought
offline because of a disk controller failure; the entire disk does not need remirroring, and only
the data changed during the failed disk??™s downtime needs to be resynced. As a result, you can
use the ASM fast mirror resync feature introduced in Oracle Database 11g.
To implement fast mirror resync, you set the time window within which ASM will not
automatically drop the disk in the disk group when a transient planned or unplanned failure
occurs. During the transient failure, ASM keeps track of all changed data blocks so that when
the unavailable disk is brought back online, only the changed blocks need to be remirrored
instead of the entire disk.
To set a time window for the DATA disk group, you must first set the compatibility level of the
disk group to 11.1 or higher for both the RDBMS instance and the ASM instance (this only needs
to be done once for the disk group):
SQL> alter diskgroup data set attribute
2 'compatible.asm' = '11.1.0.0.0';
Diskgroup altered.
SQL> alter diskgroup data set attribute
2 'compatible.
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