[SunRescue] Re: Software raid

[Kevin Loch]

Actually, you can run DiskSuite raid zero on one disk
and get much better (and quieter) performance than
without.  It must be the extra caching or some intelligent
write queueing that smooths out the seeks.

On a side note, using the "cat" device driver in FreeBSD
to stripe two disks, I was able to achieve exactly twice
the throughput of a single disk under careful measurement.
I was impressed with that since it was a software only
solution.

Of course those examples are with raid 0.
Raid 5 is what kills you on performance.  If you have
the disks, try raid0+1 (the optimum for high write
counts anyway).  

KL

Robert Novak wrote:
> 
> I thought I heard a "Joshua D. Boyd" say:
> >
> > Has anyone here ever tried running software raid-5?  I need a new file
> > server I guess (my current PeeCee one doesn't have enough drive bays or
> > PCI slots).  Sun is an option, but PC is more likely.
> 
> I've used Solstice Disksuite for RAID on Solaris, and it functions for
> RAID-5, but does not perform too well. Of course I was building it up for
> a higher demand environment than your typical home system (100 software
> developers) so the hits I saw were more profound.
> 
> As another poster suggested, the Mylex PCI RAID cards can be had cheaply
> (I have three, 3-channel wide scsi with 16mbyte cache, contact me offlist
> if you're interested in one so I can dig it out) and if your OS supports
> it you should be in good shape. They will give you better performance
> although you would have to have a full-length pci slot available.
> 
> > Anyway, I'm wondering what the possibilities for software raid-5 are.  I
> > know the computations are fairly intensive, but would something like a
> > dual processor pentium (say dual 166) be able to keep up fast enough to
> > saturate 100 mbit? How about an Ultra 1?  Ultra 5?
> 
> If you really need 100mbps of nfs traffic, fairly consistently, you should
> be able to justify hardware raid.
> 
> > Am I going to find that the cost of a good enough computer will be higher
> > than the cost of a hardware solution?
> 
> I don't remember the numbers--could dig them out of 3-year-old email
> archives if needed--but I had an Ultra 450, 4x300mhz cpu, 12 drives on 6
> scsi buses (2 each) on 3 pci buses (1 card/2 scsi buses per pci bus) and
> it still was not viable for my environment. I gave up and went to an
> external hardware raid device. Any more I won't even touch software
> RAID-5. RAID 0/1/0+1/1+0 is fine in software but beyond that, I won't even
> give it the time of day. I have not used veritas raid5 so it might be
> better, but for the cost of a license I can get a hardware controller :)
> 
> --Rob
> 
> --
> Robert Novak, Indyramp Consulting * rnovak at indyramp.com * indyramp.com/~rnovak
>         "And it's been a long December and there's reason to believe
>            Maybe this year will be better than the last...." -- counting crows
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-- 
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|  Kevin M. Loch                 |    Phone:    703.352.7501x512
|  Open Systems Associates, Inc. |    email:    kloch at kl.net
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