Processor failures in post-petascale settings are common occurrences. The traditional fault-tolerance solution, checkpoint-rollback, severely limits parallel efficiency. One solution is to replicate application processes so that a processor failure does not necessarily imply an application failure. Process replication, combined with checkpoint-rollback, has been recently advocated by Ferreira et al. We first identify an incorrect analogy made in their work between process replication and the birthday problem, and derive correct values for the Mean Number of Failures To Interruption and Mean Time To Interruption for exponentially distributed failures. We then extend these results to arbitrary failure distributions, including closed-form solutions for Weibull distributions. Finally, we evaluate process replication using both synthetic and real-world failure traces. Our main findings are: (i) replication is less beneficial than claimed by Ferreira et al; (ii) although the choice of the checkpointing period can have a high impact on application execution in the no-replication case, with process replication this choice is no longer critical.
