Minimal Long-Term Storage Economic Model

Parameters

TB for Years


Description

A minimal model of the endowment needed to store one terabyte on disk forever under a set of assumptions which can be adjusted. It is an initial, greatly simplified version of earlier work by the LOCKSS Program and students at the Storage Systems Research Center of UC Santa Cruz. This work was published here in 2012 and in later papers (see here).

The endowment is the money which, deposited with the data and invested at interest, suffices to pay for the storage of (in this case) a terabyte "forever", which in this model is 100 years.

Parameters

This model's parameters are as follows.

Media Cost Factors

DriveCost
The initial cost per drive, assumed constant in real dollars.
DriveTeraByte
The initial number of TB of useful data per drive (i.e. excluding overhead).
KryderRate
The annual percentage by which DriveTeraByte increases.
DriveLife
Working drives are replaced after this many years.
DriveFailRate
Percentage of drives that fail each year.

Infrastructure Cost factors

SlotCost
The initial non-media cost of a rack (servers, networking, etc) divided by the number of drive slots.
SlotRate
The annual percentage by which SlotCost decreases in real terms.
SlotLife
Racks are replaced after this many years

Running Cost Factors

SlotCostPerYear
The initial running cost per year (labor, power, etc) divided by the number of drive slots.
LaborPowerRate
The annual percentage by which SlotCostPerYear increases in real terms.
ReplicationFactor
The number of copies. This need not be an integer, to account for erasure coding.

Financial Factors

DiscountRate
The annual real interest obtained by investing the remaining endowment.

Assumptions