Date: Wed, 24 Feb 1999 15:12:48 -0500 (EST) From: Maxwell Spangler <maxwell@clark.net> To: Doug Ledford <dledford@redhat.com> Cc: AIC7xxx@FreeBSD.ORG Subject: Re: Adaptec 7890 and RAID portIII RAID controller Linux Support Message-ID: <Pine.LNX.4.04.9902241451370.23862-100000@maxwax.doghouse.com> In-Reply-To: <36998122.9566C573@redhat.com>
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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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe aic7xxx" in the body of the message
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