Tuesday, March 28, 2017

Understanding SolidFire Capacity

To calculate the effective capacity available, follow this formula:

  • Error Threshold (#3) minus Used Capacity (#1) = Available physical space
    • In the example below, 86.24TB - 48.41TB = 37.83TB
  • Multiply Redupe Ratio * Compression Ratio, then divide by 2 (for Double Helix)
    • In the example below, (1.81 * 1.79)/2 = 1.62:1
  • Multiply the results of (a) and (b)
    • 37.83TB * 1.62 = 61.29TB

*This calculation assumes the current rate of dedupe and compression will continue
*This calculates capacity until the Error Threshold is reached, not the Total Capacity.

From ActiveIQ, our cloud monitoring tool:

  1. Used Capacity.  This is the capacity physically taken up on disk by data.  After dedupe, compression, and double helix occur, this number is the end result.
  2. Warning Threshold.  This is an adjustable alert threshold to alert that you’re approaching the Error Threshold.
  3. Error Threshold.  This is the point after which the system cannot rebuild the second copy of data after a node loss.  This is calculated by subtracting one node’s physical block capacity from the Total Capacity.
  4. Total Capacity.  This is the raw physical space on disk.  In this example, 1.92TB * 9 SSD’s * 5 nodes = 86.42TB.

From the SolidFire GUI:
      5. Block Remaining.  This is calculated subtracting the Used Capacity (#1) from Total Capacity (#4).
      6. Block Capacity until Warning.  This is calculated subtracting the Used Capacity (#1) from Warning Threshold (#2).


***Bonus***

       7. In ActiveIQ, under Reporting | Cluster Efficiency, hover over the graph to view the dedupe and compression ratios.  In this lab system, 1.81 * 1.79 = 3.24:1

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