Software Defined Storage

IBM Storage Insights: Capacity changes for devices with FlashCore Modules

By John Walsh posted Fri November 29, 2019 07:27 AM


Originally posted by: John Walsh (ID)

In the fourth quarter 2019 release of IBM Storage Insights (and IBM Spectrum Control Version 5.3.5), we're changing how we report capacity for storage systems that use hardware compression. 


Capacity usage is now reported based on the physical rather than the effective capacity of the storage system. 


This change will make it easier to see when you are running out of space on the device.

Watch this video to learn about the changes.


What storage systems are impacted:

  • Storage systems like FlashSystem 9100, FlashSystem 900, and Storwize® V7000 Gen3, which contain IBM FlashCore® Modules with hardware compression

  • SAN Volume Controller and Storwize storage systems that are configured as storage virtualizers, and which use back-end storage systems with hardware compression

Two notions of capacity for these storage systems:

  • Physical (or real) capacity of the device

  • Effective (or potential) capacity that the device is capable of, given the data reduction savings that are achieved with the FlashCore Modules, which automatically compress data

Example: A device with FlashCore Modules has a physical capacity of 10TiB but might have effective capacity of 25 TiB after compression.


After the IBM Storage Insights update:

  • Capacity views, reports, and historical charts show a sharp drop in the values for capacity. That's because capacity values are now measured based on the physical capacity rather than the effective capacity. The capacity savings achieved by hardware compression are no longer included.

  • Capacity values such as shortfall percentage and zero capacity now use physical capacity rather than effective capacity.

  • The sharp drop in reported capacity values might cause capacity alerts to trigger

Pro tip: Review the alert threshold values for block storage systems and pools. Since the capacity values are now based on physical capacity, you might want to reduce the threshold value at which the alerts fire for your affected devices.


In the following chart simulation, the "Before Update" values represent the effective capacity and the "After Update" values represent the physical capacity, which is lower.



Alert updates

This update affects capacity alerts for storage systems and pools in IBM® Storage Insights Pro. After the update completes, you'll see a sharp drop in the reported capacity values and that might cause the following alerts to trigger:   

  • Pool Capacity
  • Physical Allocation
  • Available Pool Space
  • Allocated Space

New alerts are available to monitor the effective capacity values. Check for alerts that begin with Effective.

Pro tip: For devices that use hardware compression, you can now define alerts to monitor physical capacity at the pool level. Previously, it was only possible to monitor physical capacity at the RAID array level.


Block Storage Systems and Pools

Two sets of capacity values are now shown for storage systems and pools. 

1. The existing capacity columns (highlighted below) now show physical capacity values. 




2. New columns were added to show the effective capacity based on the data reduction savings that are achieved with hardware compression. Just check the column names in the GUI that begin with Effective, such as Effective Capacity (GiB) and Effective Used Capacity (%).


For a full breakdown of the all the changes to the Pools and Block Storage Systems views, see Capacity reporting changes for devices that use hardware compression in the IBM Knowledge Center.


Changes to historical charting

In historical capacity charts for storage systems and pools, you'll see a sharp drop in the values for capacity, allocated space, and available pool space. That's because capacity values are now measured based on the physical capacity rather than the effective capacity.





Changes to capacity overview chart

The Physical Capacity chart for storage systems now shows physical capacity values rather than effective capacity. After the update, you'll see a sharp drop in the allocated, unallocated, and total space values that are shown on the chart.





Useful links

For more information about these changes, see Capacity reporting changes for devices that use hardware compression in the IBM Knowledge Center.

Check out the what's new topic in the IBM Knowledge Center for an overview of all the latest features in IBM Storage Insights.


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