Expert Oracle Exadata - Parent Directory

CHAPTER 14 STORAGE LAYOUTparameter instructs CellCLI to use only disk-based cell disks. Just in case you are wondering, FlashCache modules are also presented as cell disks (of type FlashDisk) and may be used for creating griddisks as well. We’ll discuss flash disks later on in this chapter. The following command shows the griddisks created.CellCLI> list griddisk attributes name, cellDisk, diskType, size -where name like 'TEST_.*'TEST_CD_00_cell03 FD_00_cell03 HardDisk 96MTEST_CD_01_cell03 FD_01_cell03 HardDisk 96M…TEST_CD_10_cell03 FD_10_cell03 HardDisk 96MTEST_CD_11_cell03 FD_11_cell03 HardDisk 96MGrid Disk SizingAs we discussed earlier, grid disks are equivalent to ASM disks. They are literally the building blocks ofthe ASM disk groups you will create. The SYSTEM_DG disk group is created when Exadata is installed on asite. It is primarily used to store the OCR and voting files used by Oracle clusterware (GridInfrastructure). However, there is no reason SYSTEM_DG cannot be used to store other objects such astablespaces for the Database File System (DBFS). In addition to the SYSTEM_DG, (or DBFS_DG) disk group,Exadata is also delivered with DATA and RECO disk groups to be used for database files and Fast RecoveryAreas. But these disk groups may actually be created with whatever names make the most sense for yourenvironment. For consistency, this chapter uses the names SYSTEM_DG, DATA_DG and RECO_DG. If you areconsidering something other than the “factory defaults” for your disk group configuration, rememberthat a main reason for using multiple ASM disk groups on Exadata is to prioritize I/O performance. Thefirst grid disks you create will be the fastest, resulting in higher performance for the associated ASM diskgroup.■ Note: When Exadata V2 rolled out, SYSTEM_DG was the disk group used to store OCR and voting files for theOracle clusterware. When Exadata X2 was introduced, this disk group was renamed to DBFS_DG, presumablybecause there was quite a bit of usable space left over that made for a nice location for a moderately sized DBFSfile system. Also, the other default disk group names changed somewhat when X2 came out. The ExadataDatabase Machine name was added as a postfix to the DATA and RECO disk group names. For example, themachine name for one of our lab systems is ENK. So DATA became DATA_ENK, and RECO became RECO_ENK.By the way, Oracle recommends you create a separate database for DBFS because it requiresinstance parameter settings that would not be optimal for typical application databases.Some of the most common ASM disk groups areSYSTEM_DG: This disk group is the location for clusterware’s OCR and voting files.It may also be used for other files with similar performance requirements. ForOCR and voting files, normal redundancy is the minimum requirement.Normal redundancy will create 3 voting files, and 3 OCR files. The voting filesmust be stored is separate ASM failure groups. Recall that on Exadata, each479