3.5.3.2 Disable Write-Back PMEM Cache

Use these steps if you need to disable Write-Back PMEM cache on the storage servers.

You do not have to stop the cellsrv process or inactivate grid disks when disabling Write-Back PMEM cache. However, to reduce the performance impact on the application, disable the Write-Back PMEM cache during a period of reduced workload.

1. Validate all the Physical Disks are in NORMAL state before modifying PMEM 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. Flush the PMEM cache.

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

   The PMEM cache flushes the dirty data to the lower layer Write-Back Flash Cache.

3. Check that the flushing operation for the PMEM cache has completed.

   The flushing process is complete when the PMEM devices do not show up in the cachedBy attribute for the grid disks.

   CellCLI> LIST GRIDDISK ATTRIBUTES name, cachedBy
   DATA_CD_00_cel01     FD_00_cel01
   DATA_CD_01_cel01     FD_01_cel01
   DATA_CD_02_cel01     FD_03_cel01
   DATA_CD_03_cel01     FD_02_cel01
   DATA_CD_04_cel01     FD_00_cel01
   DATA_CD_05_cel01     FD_02_cel01
   ...
   

4. Drop the PMEM cache.

   # dcli -g cell_group -l root cellcli -e drop pmemcache all 

5. Set the pmemCacheMode attribute to writethrough.

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

6. Re-create the PMEM cache.

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

7. Verify the pmemCacheMode has been set to writethrough.

   CellCLI> LIST CELL ATTRIBUTES pmemcachemode
      WriteThrough