[mythtv-users] Bad News for me...a warning to all

[Jarod C. Wilson]

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On Friday 23 April 2004 17:29, Debabrata Banerjee wrote:
> Athlon MP 2800 w/512K cache. Those numbers are pure cpu power, has nothing
> to do with drives.

Not sure what Nathan's proc was, but the numbers I get on my mere Athlon 800 
file server are better than his... Yes, those numbers are sort of cpu-bound, 
since this is the speed with which checksumming can occur, not the speed at 
which data can be read and written, something that didn't occur to me when 
spouting off.

> But I have 6 maxtor 160GB 5200 RPM FDB drives, on a 760mpx board w/66Mhz
> pci. Which I don't recommend, this board isn't stable with all the stuff I
> want to put in it.
>
> Multiple drives per bus is absolutely fine.

I'd have to say it isn't absolutely fine. Passable, perhaps. You can do it, 
but it is detrimental to optimal performance.

> You're not going to get double 
> the performance when your 32bit/33Mhz PCI bus maxes out at 132MB/s.

Okay, perhaps performance will not double with one driver per bus, but it'll 
definitely be better. But I doubt you can come close to 132MB/s with an ATA 
RAID array with multiple drives per bus. I could be mistaken, though I see 
single WD Caviar 8MB cache drives listed on storagereview.com not sustaining 
more than 36MB/s when run as a single drive on the bus. Perhaps I'll try 
sticking two on the same bus in a RAID-0 and see what happens for myself...

> Maybe 
> if you're running a 2 or 3 drive array you might gain something worth the
> trouble. It's not going to be double either. I only gain a few percent, I
> benchmarked it just for fun.

I'm not sure why you only saw a small gain... I've seen numbers that show 
considerable performance gains. It may be a ymmv case, depending on the size 
of your data set (# of files, per file size) and your read/write patterns...

> ----- Original Message -----
> From: "Jarod C. Wilson" <jcw at wilsonet.com>
> To: "Discussion about mythtv" <mythtv-users at mythtv.org>
> Sent: Friday, April 23, 2004 7:12 PM
> Subject: Re: [mythtv-users] Bad News for me...a warning to all
>
> On Friday 23 April 2004 14:51, Nathan Nottingham wrote:
> > > raid5: measuring checksumming speed
> > >    8regs     :  3262.800 MB/sec
> > >    32regs    :  2404.800 MB/sec
> > >    pIII_sse  :  3499.200 MB/sec
> > >    pII_mmx   :  5003.200 MB/sec
> > >    p5_mmx    :  6418.000 MB/sec
> >
> > Care to give a brief run down of your setup?  My RAID 5 array is
> > handicapped by having more drives than IDE buses so my numbers pale in
> > comparison:
> >
> >    8regs     :  2034.000 MB/sec
> >    32regs    :  1230.400 MB/sec
> >    pIII_sse  :  2221.600 MB/sec
> >    pII_mmx   :  2004.800 MB/sec
> >    p5_mmx    :  1993.200 MB/sec
> >
> > Or maybe I'm missing something else?
>
> Multiple driver per ATA bus will absolutely DESTROY performance. ATA is
> absolute crap when it comes to multiple devices per bus. Get a PCI ATA card
> for about $30, add it to your setup, and performance should at LEAST
> double.
>
> http://www.tldp.org/HOWTO/Software-RAID-HOWTO-4.html

- -- 
Jarod C. Wilson, RHCE

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