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Determining and enabling volume write-caching eligibility for Flash Pool aggregates

Understanding whether the FlexVol volumes associated with an aggregate are eligible for write caching can help you ensure that the volumes with high performance requirements can get the maximum performance improvement from having their associated aggregate converted to a Flash Pool aggregate.

About this task

Flash Pool aggregates employ two types of caching: read caching and write caching. Read caching is available for all volumes. Write caching is available for most volumes, but might be disabled for some volumes due to an internal ID collision. You determine write caching eligibility to help you decide which aggregates are good candidates to become Flash Pool aggregates.

You do not need any SSDs to complete this procedure.


  1. Attempt to enable the Flash Pool capability on the aggregate: storage aggregate modify aggr_name -hybrid-enabled true
  2. Take the applicable action based on the result of Step 1:
    If... Then...
    The Flash Pool capability is successfully enabled Disable the Flash Pool capability again: storage aggregate modify aggr_name -hybrid-enabled false

    You have completed this task. All of the volumes in the aggregate are eligible for write caching.

    Data ONTAP displays an error message telling you that the aggregate cannot be converted to a Flash Pool aggregate Determine which volumes are not eligible: volume show -volume * -fields hybrid-cache-write-caching-ineligibility-reason -aggregate aggr_name

    Each volume in the aggregate is listed, along with its reason for ineligibility if it is ineligible. Eligible volumes display a hyphen ("-").

  3. Your next steps depend on your requirements for the ineligible volumes:
    If you... Then...
    Do not need write caching enabled on the ineligible volumes You have completed this task. You must use the -force-hybrid-enabled option when you convert the aggregate to a Flash Pool aggregate.
    Need write caching enabled on the ineligible volumes You must move (or copy and delete) all but one of each set of volumes with the same conflicting ID to another aggregate and then move them back until no more volumes show an ID conflict.

Example with ID collisions

The following example shows the system output when there are ID collisions:

clus1::> vol show -volume * -fields hybrid-cache-write-caching-ineligibility-reason  -aggregate aggr1
  (volume show)
vserver volume   hybrid-cache-write-caching-ineligibility-reason
------- -------- -----------------------------------------------
vs0     root_vs0 -
vs0     vol1     -
vs0     vol2     "ID Collision(27216)"
vs0     vol3     "ID Collision(27216)"
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