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Determine Flash Pool candidacy and optimal cache size in ONTAP

Contributors netapp-thomi netapp-lenida netapp-dbagwell TimMcGue netapp-aherbin
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Before converting an existing local tier to a Flash Pool local tier, you can determine whether the local tier is I/O bound and the best Flash Pool cache size for your workload and budget. You can also check whether the cache of an existing Flash Pool local tier is sized correctly.

Note Prior to ONTAP 9.7, System Manager uses the term aggregate to describe a local tier. Regardless of your ONTAP version, the ONTAP CLI uses the term aggregate. To learn more about local tiers, see Disks and local tiers.
Before you begin

You should know approximately when the local tier you are analyzing experiences its peak load.

Steps

  1. Enter advanced mode:

    set advanced

  2. If you need to determine whether an existing local tier would be a good candidate for conversion to a Flash Pool local tier, determine how busy the disks in the local tier are during a period of peak load, and how that is affecting latency:

    statistics show-periodic -object disk:raid_group -instance raid_group_name -counter disk_busy|user_read_latency -interval 1 -iterations 60

    You can decide whether reducing latency by adding Flash Pool cache makes sense for this local tier.

    The following command shows the statistics for the first RAID group of the local tier “aggr1”:

    statistics show-periodic -object disk:raid_group -instance /aggr1/plex0/rg0 -counter disk_busy|user_read_latency -interval 1 -iterations 60

  3. Start Automated Workload Analyzer (AWA):

    storage automated-working-set-analyzer start -node node_name -aggregate aggr_name

    AWA begins collecting workload data for the volumes associated with the specified local tier.

  4. Exit advanced mode:

    set admin

    Allow AWA to run until one or more intervals of peak load have occurred. AWA collects workload statistics for the volumes associated with the specified local tier, and analyzes data for up to one rolling week in duration. Running AWA for more than one week will report only on data collected from the most recent week. Cache size estimates are based on the highest loads seen during the data collection period; the load does not need to be high for the entire data collection period.

  5. Enter advanced mode:

    set advanced

  6. Display the workload analysis:

    storage automated-working-set-analyzer show -node node_name -instance

  7. Stop AWA:

    storage automated-working-set-analyzer stop node_name

    All workload data is flushed and is no longer available for analysis.

  8. Exit advanced mode:

    set admin