3.4.5.2 Enabling Write Back Flash Cache on a Rolling Basis for Software Versions Lower Than 11.2.3.3.1

You can enable Write Back Flash Cache on a rolling basis.

To modify the Flash Cache attribute from writethrough to writeback, the Flash Cache must be dropped first. For Oracle Exadata System Software releases prior to 11.2.3.3.1, you must stop cell services or inactivate grid disks when enabling Write Back Flash Cache.

There is a shell script to automate enabling and disabling Write Back Flash Cache. Refer to My Oracle Support document FAQ2730 for the script and additional information.

Note:

Any time the Flash Cache is dropped and re-created, there is a performance impact for database operations. While the Flash Cache is being repopulated, there are more cache misses, which impacts database performance.

Oracle Grid Infrastructure homes and Oracle Database homes must at release 11.2.0.3 BP9 or higher to use write-back Flash Cache. Refer to Exadata Database Machine and Exadata Storage Server Supported Versions (My Oracle Support Doc ID KB153930) for the minimum release requirements for Oracle Exadata System Software, Oracle Grid Infrastructure home, and Oracle Database home.

1. Log in as the root user to the first cell to be enabled for Write Back Flash Cache.
2. Check that the Flash Cache is in normal state and no flash disks are degraded or in a critical state.

   # cellcli -e LIST FLASHCACHE detail
   

3. Drop the Flash Cache on the cell.

   # cellcli -e DROP FLASHCACHE
   

4. Inactivate the grid disks on the cell.

   # cellcli -e ALTER GRIDDISK ALL INACTIVE
   

5. Shut down CELLSRV services.

   # cellcli -e ALTER CELL SHUTDOWN SERVICES CELLSRV
   

6. Set the flashCacheMode attribute to writeback.

   # cellcli -e "ALTER CELL FLASHCACHEMODE=writeback"
   

7. Restart cell services.

   # cellcli -e ALTER CELL STARTUP SERVICES CELLSRV
   

8. Reactivate the grid disks on the cell.

   # cellcli -e ALTER GRIDDISK ALL ACTIVE
   

9. Re-create the Flash Cache.

   # cellcli -e CREATE FLASHCACHE ALL
   

10. Check the status of the cell.

    # cellcli -e LIST CELL DETAIL | grep flashCacheMode
    

    The flashCacheMode attribute should be set to writeback.

11. Check the grid disk attributes asmDeactivationOutcome and asmModeStatus before moving to the next cell using the following command:

    CellCLI> LIST GRIDDISK ATTRIBUTES name,asmdeactivationoutcome,asmmodestatus
    

    The asmDeactivationOutcome attribute should be yes, and the asmModeStatus attribute should be online.

12. Repeat the preceding steps on the next cell.