Setting replacement slice

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Slices are reallocated when storage resources are removed from the pool and replaced with a new resource.

At a high level, all the slice data on the replaced sets is moved to the remaining and new sets in the pool. The slices are reallocated according to the capacity of the remaining storage resources.

For example, a storage pool has three sets: 10 PB, 20 PB, and 25 PB for a total of 55 PB. The percentages of each set are:
  1. 10 PB / 55 PB = 18.18%
  2. 20 PB / 55 PB = 36.36%
  3. 25 PB / 55 PB = 45.45%

The storage pool is storing 40 PB of data. Based on the set capacities and their respective percentage of the total capacity, this much data is stored on each set (40 PB / 55 PB = 72.72% full):

  1. 10 PB * (40 PB / 55 PB) = 7.27 PB
  2. 20 PB * (40 PB / 55 PB) = 14.54 PB
  3. 25 PB * (40 PB / 55 PB) = 18.18 PB

The user decides to replace the 10 PB set with a new, larger device set of 30 PB. After initiating replacement, the percentages of each set are:

  1. 30 PB / 75 PB = 40.00%
  2. 20 PB / 75 PB = 26.67%
  3. 25 PB / 75 PB = 33.33%

The 7.27 PB stored on the 1-PB set reallocates onto the replacement set. In addition, because the 20 PB and 25 PB sets now make up a lesser percentage of the total capacity, some of the slice data is reallocated to the 30 PB set. In the end, the three sets should have a percentage of stored data roughly equal to their percentage of the total capacity.

  1. 30 PB * (40 PB / 75 PB) = 15.99 PB
  2. 20 PB * (40 PB / 75 PB) = 10.67 PB
  3. 25 PB * (40 PB / 75 PB) = 13.33 PB