Why does SAP only recommend SETALL if it has disadvantages on SAN-storage? Or are there signifant advantages in other areas that should outperform the disadvantages in backup performance.
Stefan Koehler gave an excellent answer on your question. FILESYSTEM_OPTIONS=SETALL allows oracle to use CIO capabilities of JFS2 file system in addition to async i/o:
- async i/o;
- bypass file system cache (Oracle already use its buffer cache for caching therefore file system cache is only overhead in memory consumption and unneccessary CPU cycles for its maintain);
- avoiding i-node locking (multiple threads may simultaneously perform reads and writes on a shared file).
Disadvantages: use of CIO disables any file system mechanisms that depend on the use of file system cache, e.g. sequential read-ahead (applications that perform a significant amount of sequential read I/O may experience degraded perfromance).
