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Article Number: 000029068

Data Domain: Data Domain Restorers (DDRs) may alert indicating that the 'Current cache tier size is less than what the system is licensed for'

Summary: This article describes the cause and steps to resolve alerts indicating that 'Current cache tier size is less than what the system is licensed for'.

Article Content


Data Domain Operating System (DDOS) 6.0 introduces a new tier of storage known as the cache tier. This storage:
  • Is comprised of dedicated SSD devices installed in either the head unit of the system or an external ES30 shelf (depending on platform and configuration)
  • Is used to cache metadata used by the Data Domain File System (DDFS) to improve system performance
  • Is only supported on certain platform types (for example EOS and DD9500/9800 systems)
If a system is licensed for a cache tier but no such tier has been created (or it is smaller than the licensed size) a corresponding alert may be posted, i.e.:
Id      Post Time                  Severity   Class             Object                Message                                                                                 
-----   ------------------------   --------   ---------------   -------------------   ----------------------------------------------------------------------------------------
m0-2    Mon Jul 18 13:49:28 2016   WARNING    Storage                                 EVT-STORAGE-00025: Current cache tier size is less than what the system is licensed for.


This article describes the cause and resolution of the above alert.


This alert is caused by having a Data Domain Restorer (DDR) which is licensed for a cache tier of a certain size but either:
  • The cache tier does not exist
  • The cache tier is smaller than the licensed size


  • Check licenses on the DDR to confirm the size of the cache tier for which it is licensed:
# elicense show
Capacity licenses:
##  Feature              Shelf Model   Capacity    Mode        Expiration Date
--  ------------------   -----------   ---------   ---------   ---------------
3    SSD-CAPACITY        n/a           2.91 TiB    permanent   n/a
--  ------------------   -----------   ---------   ---------   ---------------

  • Confirm the current size of the cache tier and any devices which are available for use in the cache tier:
# storage show all
Cache tier details:
Disk          Disks     Count   Disk         Additional
Group                           Size         Information
-----------   -------   -----   ----------   -----------
(available)   1.5-1.8   4       745.2 GiB
-----------   -------   -----   ----------   -----------

Current cache tier size: 0.0 TiB

In the above example we can see that:

The system is licensed for a cache tier of 2.91 TiB
The cache tier is currently 0.0 TiB in size
There are four 745.2 GiB disks available for addition to the cache tier (note that 4 x 745.2 GiB = 2.91 TiB)
  • Add available disks to the cache tier:
# storage add disks 1.5,1.6,1.7,1.8 tier cache

This allows the cache tier to be created (or increased in size), after which the alert should clear.
NOTE: If the cache tier is newly created it takes some time for it to be populated with the required DDFS metadata. This population is done in the background while the system is running as normal; however, increased performance (due to the cache tier) is not fully realized until cache tier population is complete.

Article Properties

Affected Product

Data Domain


Data Domain

Last Published Date

23 Aug 2023



Article Type