IOVec blocks are allocated with 1KB step. So for the 1-element time-series only 1KB will be allocated. When series won't fit into 1KB the second 1KB chunk will be allocated and so on, until IOVec block won't be filled. This means that the numbers in the table above are worst case numbers. On average IOVec blocks are half full on every level. For instance, this means that for the series that occupies from 128MB to 4GB on disk Akumuli may need to use 5-20KB for the memory-resident component. Averaged for high number of individual time-series that will give us 11KB of RAM per/series in this specific scenario.