Expert Oracle Exadata - Parent Directory

CHAPTER 14 STORAGE LAYOUT1 st Grid Disk(DATA_DG Disk group)3 rd Grid Disk(STAGE_DG Disk Group)2 nd Grid Disk(RECO_DG Disk Group)Figure 14-6. The default allocation policyTable 14-1 shows the performance effect on the ASM disk groups from the first to the last grid diskcreated when using the default allocation policy. You won’t find the term “I/O Performance Rating” inthe Oracle documentation. It’s a term I’m coining here to describe the relative performance capabilitiesof each disk group due to its location on the surface of the physical disk drive.Table 14-1. I/O Performance – Default Allocation PolicyASM Disk GroupI/O Performance RatingDATA_DG 1RECO_DG 2STAGE_DG 3Fourth disk group 4SYSTEM_DG 5InterleavingThe other policy, interleaving, attempts to even out performance of the faster and slower tracks byallocating space in an alternating fashion between the slower and faster tracks of the disks. This is doneby splitting each cell disk into two regions, an outer region and an inner region. Grid disks are slices ofcell disks that will be used to create ASM disk groups. For example, the following command creates 12grid disks (one per physical disk; see Figure 14-4) on Cell03 to be used for the DATA_DG disk group:475