Software RAID 5 or something else?

[Alan Cox]

> So considering that, what do you gain from dedicated hardware for RAID?  
> You get a commercially supported RAID software and hardware package, and 
> you get to unload a bit of CPU from the main system.

The big thing it saves you on in RAID 1 & 5 is memory bandwidth, and in
RAID5 doubly so for the XOR costs. The second thing it helps with is bus
bandwidth as each chunk of data crosses the PCI(X) bus once. In the PCI
world that really helped, PCI-X it's less clear.

The last benefit is a battery backed cache.

> Considering that the CPU on the card at max performance is probably 1/3 
> of a core from a modern CPU, then that is not really much of a savings.
> 
> The real consideration for RAID 5 is survival.  In either situation you 
> have to have a spare drive, and you have to consider availability of new 
> drives to match them in the future.

Bigger ones will do

Alan