[Beowulf] PetaBytes on a budget, take 2

[Greg Lindahl]

On Thu, Jul 21, 2011 at 08:03:58PM -0400, Ellis H. Wilson III wrote:

> Used in a backup solution, triplication won't get you much more
> resilience than RAID6 but will pay a much greater performance penalty to
> simply get your backup or checkpoint completed.

Hey, if you don't see any benefit from R3, then it's no surprise that
you find the cost too high. Me, I don't like being woken up in the
dead of the night to run to the colo to replace a disk. And I trust my
raid vendor's code less than my replication code.

> Additionally, unless you have a ton of these boxes you won't get
> some of the important benefits of Hadoop such as rack-aware
> replication placement.

Most of the benefit is achieved from machine-aware replication
placement: the number of PDU and switch failures is much smaller than
the number of node failures, which is much smaller than the number of
disk device failures.

-- greg