Expert Oracle Exadata - Parent Directory

CHAPTER 14 STORAGE LAYOUTsystem. But just because you can do something, doesn’t mean you should. Storage cells are theworkhorse of Exadata. Each cell supports a finite data transfer rate (MBPS) and number of I/O’s persecond (IOPS). Reducing the storage cell footprint of your database environment directly impacts theperformance your database can yieldTable 14-6. Performance Capabities of Exadata Storage CellsMBPS & IOPS by Device Type Quarter Rack Half Rack Full RackDisk Transfer Bandwidth SASSATA4.5 GB/s2.5 GB/s10.5 GB/s6 GB/s21 GB/s12 GB/sFlash Disk Transfer Bandwidth 11 GB/s 25 GB/s 50 GB/sDisk IOPSSATASAS10,8004,30025,00010,00050,00020,000Flash Disk IOPS 225,000 500,000 1,000,000■ Note: Exadata V2 offered two choices for disk drives in the storage cells, SATA, and SAS. With Exadata X2, theSATA option has been replaced with High Capacity SAS drives that have storage and performance characteristicsvery similar to those of the SATA drives they replaced. So now, with X2, your storage options are High Capacityand High Performance SAS drives.Cell SecurityIn addition to isolating storage cells by their network address, Exadata also provides a way to secureaccess to specific grid disks within the storage cell. An access control list (ACL) is maintained at thestorage cell, and grid disks are defined as being accessible to specific ASM clusters and, optionally,databases within the ASM cluster. If you’ve already logged some time working on your Exadata system,chances are you haven’t noticed any such access restrictions. That is because by default, cell security isopen, allowing all ASM clusters and databases in the system access to all grid disks. Cell security controlsaccess to grid disks at two levels, by ASM cluster and by database:ASM-Scoped Security: ASM-scoped security restricts access to grid disks byASM cluster. This is the first layer of cell security. It allows all databases in theASM cluster to have access to all grid disks managed by the ASM instance. Forexample, an Exadata full rack configuration can be split so that four databaseservers and seven storage cells can be used by Customer-A, and the other fourdatabase servers and seven storage cells can be used by Customer-B.Database-Scoped Security: Once ASM-scoped security is configured, access togrid disks may be further controlled at the database level using databasescopedsecurity. Database-scoped security is most appropriate when databaseswithin the ASM cluster should have access to a subset of the grid disks managed487