Re: limits on raid

[david]

On Tue, 19 Jun 2007, Lennart Sorensen wrote:

> On Mon, Jun 18, 2007 at 02:56:10PM -0700, david@xxxxxxx wrote:
> > yes, I'm useing promise drive shelves, I have them configured to export
> > the 15 drives as 15 LUNs on a single ID.
> >
> > I'm going to be useing this as a huge circular buffer that will just be
> > overwritten eventually 99% of the time, but once in a while I will need to
> > go back into the buffer and extract and process the data.
>
> I would guess that if you ran 15 drives per channel on 3 different
> channels, you would resync in 1/3 the time.  Well unless you end up
> saturating the PCI bus instead.
>
> hardware raid of course has an advantage there in that it doesn't have
> to go across the bus to do the work (although if you put 45 drives on
> one scsi channel on hardware raid, it will still be limited).

I fully realize that the channel will be the bottleneck, I just didn't 
understand what /proc/mdstat was telling me. I thought that it was telling 
me that the resync was processing 5M/sec, not that it was writing 5M/sec 
on each of the two parity locations.

David Lang
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