Adaptec 7890 and RAID portIII RAID controller Linux Support

[Torry Akins]

Hi,

I currently setup a linux data acquistion system with 4 9.1G Cheetah Drives on two
controllers (2x2).  I can only report on RAID0, but I wrote a gigabyte file to
this guy at 53 Mbytes/sec.  70% of the CPU was used in doing this, but I don't
know how much of this was due to software RAID and how much is due to the fact
that I'm passing 53 MB/sec into kernel space.

I kind of new to alot of this,

Torry Akins

Maxwell Spangler wrote:

> On Mon, 11 Jan 1999, Doug Ledford wrote:
>
> > To sum up my impressions, hardware RAID is a waste of money.  It doesn't
> > buy speed any more (it used to when a hot server was a 486/33 and you
> > had an i960 chip on the RAID controller).  The newest RAID5 and RAID1
> > code from Ingo Molnar is *quite* reliable and pretty much on par with
> > what you would get in a hardware raid array.  The real reason for raid
> > used to be reliability in the face of failure.  Any more, with as
> > reliable as the software has gotten, I consider the hardware raid arrays
> > simply another possible point of failure.  I would go software raid if I
> > were you.
>
> But isn't offloading processing of any sort to a specialised chip or device a
> good thing?  (Considering modern day hardware, not older stuff)
>
> For example: (Completely fictional comparison example)
>
> A PII-233 performing software OpenGL can produce 500 3D video operations in
> one second, but it takes 30% of the CPU's processing time to do so.
>
> A second PII-233 performing the same task with the assistance of a hardware 3D
> device can perform the same number of operations, but reduce the amount of CPU
> processing time to 5%.
>
> Case #2 would be better, and for years a lot of us have used SCSI instead of
> IDE (PIO IDE, not udma EIDE) because this was better.  As you pointed out, in
> the days of 386/486 CPUs, offloading to SCSI cards, network cards, video
> cards, was not only a good thing but required.  Wouldn't that concept scale to
> modern systems but just allow us to go even faster?
>
> I wonder if you are saying that:
>
> * Modern CPUs have CPU cycles to spare for most users and Ingo's SW RAID code
> is efficient and can utilize those cycles without much overall impact?
>
> * hardware raid controllers aren't don't have the same ratio of power compared
> to the host CPU as they used to?  Can a PII-450 running SW RAID outperform a
> hardware RAID card, for example?
>
> I wonder if you'd guess as to what impact the SW RAID might have in a typical
> workstation or file server environment.  If I had a nicely configured system
> that was running along fine and I added SW RAID, would be be a noticable drain
> on the CPU?
>
> How about a dedicated fileserver with 1 root/boot disk, and 6 (3x3)?  Would
> removing a "typical" or average quality/speed HW RAID solution and replacing
> it with software have much of an impact?
>
> I think your comment about recommending SW RAID over hardware just sounded too
> good to be true for me based on past years' experiences.  But then, this
> wouldn't be the first time Linux has broken commonsense ways of computing for
> something better :)
>
> -----------------------------------------------------------------------------
> Maxwell Spangler, Software Developer
> Greenbelt, Maryland USA
>
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