Expert Oracle Exadata - Parent Directory

CHAPTER 14 STORAGE LAYOUTstorage cell constitutes a failure group. This means that only normalredundancy may be used for an Exadata quarter rack configuration (3 storagecells/failure groups). Only in half rack and full rack configurations (7 or 14storage cells/failure groups), are there a sufficient number of failure groups tostore the required number of voting and OCR files required by highredundancy. Table 14-3 summarizes the storage requirements for OCR andvoting files at various levels of redundancy. Note that External Redundancy isnot supported on Exadata. We’ve included it in the table for reference only.DATA_DG: This disk group is used for storing files associated with thedb_create_file_dest database parameter. These include datafiles, online redologs, control files, and spfiles.RECO_DG: This disk group is what used to be called Flash Recovery Area (FRA).Sometime after 11gR1 Oracle renamed it to the “Fast Recovery Area”; rumor hasit that the overuse of “Flash” was causing confusion among the marketing team.So to clarify, this diskgroup will be used to store everything corresponding tothe db_recovery_file_dest database parameter. It includes online databasebackups and copies, mirror copies of the online redo log files, mirror copies ofthe control file, archived redo logs, flashback logs, and Data Pump exports.Table 14-3. OCR & Voting File Storage RequirementsRedundancy Min # of Disks OCR Voting TotalExternal 1 300 MB 300 MB 600 MBNormal 3 600 MB 900 MB 1.5 GBHigh 5 900 MB 1.5 GB 2.4 GBRecall that Exadata storage cells are actually finely tuned Linux servers with 12 internal disk drives.Oracle could have dedicated two of these internal disks to run the operating system, but doing so wouldhave wasted a lot of space. Instead, they carved off several small partitions on the first two disks in theenclosure. These partitions, about 30 GB each, create a slight imbalance in the size of the cell disks. Thisimbalance is so small it doesn’t affect performance, but it is something that you will have to work withwhen planning your grid disk allocation strategy. Figure 14-9 illustrates this imbalance.480