Online strategies for backups

Artikel i vetenskaplig tidskrift, 2002

We consider strategies for backups from the viewpoint of competitive analysis of online problems. We concentrate upon the realistic case that faults are rare, i.e. the cost of work between two faults is typically large compared to the cost of one backup. Instead of the (worst-case) competitive ratio we use a refined and more expressive quality measure, in terms of the average fault frequency. The interesting matter is, roughly speaking, to adapt the backup frequency to the fault frequency, while future faults are unpredictable. We give an asymptotically optimal deterministic strategy and propose a randomized strategy whose expected cost beats the deterministic bound.