private DiskSpaceAllocator constructUnpooledAllocator() {
    return new DiskSpaceAllocator(false, reserveFileDir, requiredSwapSegmentsPerSize, METRICS);
  }
@return a new {@link DiskSpaceAllocator} with pooling disabled.
ambry-store/src/test/java/com/github/ambry/store/DiskSpaceAllocatorTest.java