How to flush and disable FAST Cache in CLARiiON / VNX Array ?

Product:

 

CLARiiON VNX


 

Description:

 

Procedure to flush and disable FAST Cache in CLARiiON / VNX Array.

 

Resolution:

 

The procedures below are also best practice for flushing and temporarily disabling FAST Cache, without unbinding/destroying the FAST Cache configuration and LUNs (in which case, the last step to destroy FAST Cache would not be needed).


Another reason to disable FAST Cache on certain LUNs or Pools would be to avoid it being utilized by lower priority streams of I/O, or applications unsuited to FAST Cache.

 

To selectively disable FAST Cache using Unisphere:

  1. Go to the System List view in Unisphere and select the relevant VNX or CLARiiON.
  2. Highlight the Storage tab.
    • On a CX4 (Unisphere 1.0), select "Pools/RAID Groups" from the Storage drop-down menu, which will bring up a page with two tabs: Pools and RAID Groups.  (This_CX4 > Storage > Pools/RAID Groups)
    • On a VNX (Unisphere 1.1), select "Storage Pools" from the Storage drop-down menu, which will bring up a page with two tabs: Pools and RAID Groups.  (This_VNX > Storage > Storage Configuration > Storage Pools)

 

  For FLARE LUNs (that is, a LUN in a RAID group, not a Pool): 

  1. Select the RAID Groups tab (This_VNX > Storage > Pools/RAID Groups > RAID Groups). 
  2. Select the relevant RAID Group in the upper pane, then the LUN in the lower pane. 
  3. Click the Properties button, then select the Cache tab. 
  4. There will be a check box to enable FAST Cache on this LUN, so clear/untick this box to disable FAST Cache on just this LUN.  The LUN properties view can also be reached other from menus in Unisphere, such as the LUNs or Storage Groups menus.

 

  For Pools (Virtual Provisioning), the FAST Cache is enabled or disabled for the whole Pool, rather than for individual Pool LUNs: 

  1. Select the Pools tab and highlight the required Pool. 
  2. Click the properties button in the top pane. 
  3. Go to the Advanced tab. 
  4. There will be a check box to enable FAST Cache on this LUN, so clear/untick this box to disable FAST Cache for all LUNs in this Pool.


For metaLUNs, FAST Cache must be disabled on the component LUNs:

  1. Under the Storage tab, select LUNs from the drop-down menu. (For VNX, a second LUNs button under the LUNs category should be selected.) 
  2. Change the Usage drop-down box (after Filter for) to Private LUNs and the component LUNs will be shown. 
  3. Disable FAST Cache on each private component LUN in the same way as above for FLARE LUNs.


  From naviseccli, FAST cache can be selectively disabled using the following commands: 

  • For FLARE LUNs (including metaLUN components):

    naviseccli chglun -l lun -fastcache 0

  • For Pools:

    naviseccli storagepool -modify -id poolID -fastcache off


The progress of the FAST Cache flushing can be monitored in Unisphere (System > Manage Cache > FAST cache) or using the Secure CLI:

  • For the statistics to be accurate, Statistics Logging must be enabled.
  • The following Navisphere Secure CLI command will show the amount of Dirty data (blocks where the copy in FAST in more recent than the version on the original LUN) and the total amount of data flushed to the original LUNs, since the last reboot:

    naviseccli cache -fast -info -perfData


  • In Unisphere, click on the System tab.  The 'Manage cache' link is on the side toolbar (on the left-hand side for CX4 and on the right-hand side for VNX).  This will show the FAST Cache statistics for both SP.
  • FAST Cache statistics are listed for both SP A and SP B, but the data is on the FAST Cache Enterprise Flash drives.  The distinction between SP A and B for FAST Cache, is which SP owns each LUN that has FAST Cache enabled, because it will be that SP that handles the I/O to that LUN.

    Example:

    naviseccli -h 10.20.30.40 -user user1 -password password2 -scope 0 cache -fast -info -perfData

    Output:
    Percentage Dirty SPA:  73
    MBs Flushed SPA:  10186
    Percentage Dirty SPB:  18
    MBs Flushed SPB:  374649

 

When both storage processors (SPs) reach 0% dirty on both SPs, then the FAST Cache can be destroyed in only a few seconds.

  • In Unisphere, click on the System tab.  The 'Manage cache' link is on the side toolbar (on the left-hand side for CX4 and on the right-hand side for VNX).  Click on the 'Destroy' button to globally disable FAST Cache and unbind all the FAST Cache drives.
  • To disable/destroy FAST Cache using the Secure CLI:

    naviseccli -h 10.20.30.40 cache -fast -destroy


It is also possible that when destroying FAST Cache, the operation fails to complete, despite both SP showing zero percent cache dirty.  This can be caused by FAST Cache not disabling on all of a Pool's private FLARE LUNs. In this case it is possible to clear this by enabling FAST Cache on all Pools, then disabling it again.   If this fails to clear the issue, escalate to a senior Technical Support level for further investigation.

 

 

 

For more information, Refer Knowledge Base Article emc266585 and emc251589