3.4.6.2 Disable Write Back Flash Cache for 11.2.3.3.1 or Higher

You can disable write back Flash Cache on the storage servers by changing the mode to Write Through.

With release 11.2.3.3.1 or higher, you do not have to stop the CELLSRV process or inactivate grid disks.

Note:

To reduce the performance impact on the application, disable the write back flash cache during a period of reduced workload.

1. Validate all the Physical Disks are in NORMAL state before modifying FlashCache.

   The following command should return no rows:

   # dcli –l root –g cell_group cellcli –e “LIST PHYSICALDISK ATTRIBUTES name,status”|grep –v NORMAL

2. Determine amount of dirty data in the flash cache.

   # cellcli -e "LIST METRICCURRENT ATTRIBUTES name,metricvalue WHERE name LIKE \'FC_BY_DIRTY.*\' "

3. Flush the flash cache .

   # dcli –g cell_group –l root cellcli -e "ALTER FLASHCACHE ALL FLUSH" 

4. Check the progress of the flushing of flash cache.

   The flushing process is complete when FC_BY_DIRTY is 0 MB.

   # dcli -g cell_group -l root cellcli -e "LIST METRICCURRENT ATTRIBUTES name,metricvalue WHERE name LIKE \'FC_BY_DIRTY.*\' " 

   Or, you can check to see if the attribute flushstatus has been set to Completed.

   # dcli -g cell_group -l root cellcli -e "LIST CELLDISK ATTRIBUTES name, flushstatus, flusherror" | grep FD 

5. After flushing of the flash cache completes, drop the flash cache.

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

6. Set the flashCacheMode attribute to writethrough.

   # dcli -g cell_group -l root cellcli -e "ALTER CELL flashCacheMode=writethrough"

7. Re-create the flash cache.

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

8. Verify the flashCacheMode has been set to writethrough.

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