Oracle Database 11 g - Online Public Access Catalog

362 CHAPTER 9 ■ STORAGE MANAGEMENT• Consolidation of storage management• Mirroring/triple mirroring equivalence• Striping• Mirroring across heterogeneous storage arrays• Mirroring across different storage vendors• Real application cluster supportMisconceptions of ASMMany DBAs have numerous misconceptions about ASM. By revealing “the truth” about ASM,DBAs, SAs, and SAN administrators can make cognitive decisions about implementing ASM.First, ASM does not automatically rebalance the IO. The rebalance activity of an ASM diskgrouphappens only when adding or dropping disks from the diskgroup. Second, ASMLIB is availableonly for Linux and Windows. ASMLIB is a support library for ASM that simplifies the managementand discovery of ASM disks. ASMLIB is not a requirement to implement ASM but is highlyrecommended. Third, you can implement ASM without RAC. Although ASM tends to be implementedwith RAC, it performs well in stand-alone non-RAC environments too. With ASM, Oracleinstalls and configures a lightweight cluster agent called Cluster Synchronization Services (CSS).More and more companies are adopting ASM in a single instance for ease of manageability andperformance.On the same note, DBAs, SAs, and SAN administrators may be unaware of some hiddenASM features. You can leverage ASM mirroring technologies to simulate protection equivalenceto mirroring and triple-mirroring technologies using normal and failure redundancy.RMAN and ASMKnowing RMAN is a must when considering ASM. DBAs who are not intimate with RMAN donot have a choice but to learn and become experts with RMAN. There are numerous ways totransfer files from and to ASM, but believe it or not, nothing compares in performance and easeof maintenance than RMAN. ASM has the option to utilize technologies such as WebDav orFTP in conjunction with XML DB, but this option complicates the environment and supportability.■Note Although the dbms_file_transfer PL/SQL package provides the ability to copy, get, and putdatabase-related files to/from ASM using the copy_file, get_file, and put_file procedures, RMANperformance is astronomically faster than dbms_file_transfer. In addition, the level of complexity ofdbms_file_transfer compared to RMAN doesn’t make it a preferable solution. dbms_file_transferdoes have an advantage in that it does not require a backup.Now with Oracle Database 11g, you can also use the new asmcmd copy command.