3.4.5.1 Enable Write Back Flash Cache for 11.2.3.3.1 or Higher

Enable write back Flash Cache on the storage servers to improve query response times and throughput.

For Oracle Exadata System Software release 11.2.3.3.1 or higher, you do not have to stop cell services or inactivate grid disks when changing the Flash Cache from Write Through mode to Write Back mode.

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.

1. Validate all the physical disks are in NORMAL state before modifying Exadata Smart Flash Cache.

   The following command should return no rows:

   # dcli –l root –g cell_group cellcli –e “list physicaldisk attributes name,status”|grep –v NORMAL

2. Drop the Flash Cache.

   # dcli –l root –g cell_group cellcli -e drop flashcache

3. Set the flashCacheMode attribute to writeback.

   # dcli –l root – g cell_group cellcli -e "alter cell flashCacheMode=writeback"

4. Re-create the Flash Cache.

   # dcli –l root –g cell_group cellcli -e create flashcache all 

5. Verify the flashCacheMode has been set to writeback.

   # dcli –l root –g cell_group cellcli -e list cell detail | grep flashCacheMode

6. Validate the grid disk attributes cachingPolicy and cachedby.

   # cellcli –e list griddisk attributes name,cachingpolicy,cachedby