Oracle Database 11 g - Online Public Access Catalog

CHAPTER 9 ■ STORAGE MANAGEMENT 375The fg1 failgroup is recognized as a localized read from RAC node #1 in SiteA, while it isrecognized as a remote mirror read from RAC node #2 in SiteB. Likewise, fg2 failgroup is recognizedas a localized mirror read from node #2 in SiteB and as a remote mirror read from RACnode #1 in SiteA. For the SiteA servers, the ASM instances should read from the SAN storagedevices that are from the SiteA data center:asm_preferred_read_failure_groups = data.fg1Set the parameter for the database servers in SiteB to the following:asm_preferred_read_failure_groups = data.fg2You can also configure the preferred read failure groups using Enterprise Manager DatabaseConsole. This option is the Preferred Read Failure Groups field on the Configuration tab of theASM home page, as shown in Figure 9-8. You can specify a list of failure groups delimited bycommas whose member disks will serve as the preferred read disks for this node.Figure 9-8. ASM diskgroup preferred readMonitoring Preferred ReadsOracle Database 11g adds the new column PREFERRED_READ to the V$ASM_DISK dynamic view.This column holds a Y or an N value to designate that the read is a localized and preferred readfailure group. You can also view the performance characteristics of the ASM preferred readfailure group by querying V$ASM_DISK_IOSTAT. The result of this view is to provide informationat the ASM instance level:SQL> select instname, failgroup,2 read_time, write_time, bytes_read, bytes_written3* from v$asm_disk_iostatSQL> /