[Beowulf] Mature open source hierarchical storage management

[Mark Hahn]

> It is expected that our storage will consist of a combination of fast fibre
> channel and SATA based disk and we would like to implement a system whereby

why do you think that's a good design?  consider bandwidth: you will spend
>5x as much on FC, but can easily obtain the same or higher bandwidth with
SATA given that it's so much cheaper.  (not to mention the fact that
bandwidth is rpm * recording density, and SATA is consistently a generation
or two ahead in density.  that means that a 10k rpm FC disk may sustain
120 MB/s, but a 7200 rpm SATA will do 130 over the same size (and slow down
to 90 or so on inner tracks - that is, at 3x the capacity of the FC disk...))

IMO, you'd do better to provide seeky workloads with their own filesystems,
and put everyone else on plain old SATA (made to scale to arbitrary bandwidth
and concurrency goals with, eg Lustre).  that way someone dumping a 5TB
checkpoint won't trash performance for people doing metadata or
seek-intensive stuff.  and as a side-benefit, the costliness of md/seek stuff
becomes visible to those doing it...