Expert Oracle Exadata - Parent Directory

CHAPTER 14 STORAGE LAYOUTFastest TrackSlowest TrackFigure 14-5. Disk tracksExadata provides two policies for allocating grid disk storage across the surface of disk drives. Thefirst method is the default behavior for allocating space on cell disks. It has no official name, so forpurposes of this discussion I’ll refer to it as the default policy. The other allocation policy Oracle callsinterleaving. These two allocation policies are determined when the cell disks are created. Interleavingmust be explicitly enabled using the interleaving parameter of the create celldisk command. For acomplete discussion on creating cell disks refer to chapter 8.Fastest Available Tracks FirstThe default policy simply allocates space starting with the fastest available tracks first, moving inward asspace is consumed. Using this policy, the first grid disk created on each cell disk will be given the fasteststorage, while the last grid disk created will be relegated to the slower, inner tracks of the disk surface.When planning your storage grid, remember that grid disks are the building blocks for ASM disk groups.These disk groups will in turn be used to store tables, indexes, online redo logs, archived redo logs, andso on. To maximize database performance, frequently accessed objects (such as tables, indexes, andonline redo logs) should be stored in the highest priority grid disks. Low priority grid disks should beused for less performance sensitive objects such as database backups, archived redo logs, and flashbacklogs. Figure 14-6 shows how grid disks are allocated using the default allocation policy.474