[Gllug] A SATA Raid card worth having?

[Rich Walker]

"Russell Howe" <rhowe at siksai.co.uk> writes:
>
> The CPU speeds these days probably mean the RAID calculations aren't
> going to kill them. I guess the main problem is the shift of I/O
> bottlenecks..
>
> With a hardware RAID card in a PCI slot, you do your I/O to the PCI
> card, and then it farms out the relevent I/O to whatever disks it has
> attached.
>
> With software RAID, the OS needs to do all the I/O itself, and in all
> the boxes I've used, that would mean sharing a single PCI bus to access
> either the same card multiple times, or multiple cards. I can't remember
> what the bandwidth of PCI is, but it's not hugely fast.. If you're doing
> RAID1, you effectively cut the PCI bandwidth available for disk
> operations in half (since you'll be writing everything twice).

Most PCs seem to have two PCI busses (2 or 3 PCI slots per bus).

The main issues are

* whether the second bus is at the back of the first
bus, across a bridge, or whether there are two busses coming out of the
chipset separately. 

* what is the maximum CPU-to-chipset bandwidth.

I suspect this is the kind of application where Opterons, with the
integrated memory interface and Northbridge, will shine.

cheers, Rich.

-- 
rich walker         |  Shadow Robot Company | rw at shadow.org.uk
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