IDE controller card and Fedora Core 3

[Shaffer Paul]

James' analysis is right on the money, *BUT* for a given file set,
Robert is also correct, and I've proven it with some equipment of mine.
The maximum transfer speed to/from a given machine never goes above a
certain point no matter 100Mbs, Gbit, Ultra, Ultra2, Ultra3 - doesn't
matter.  32bit PCI is the likely bottleneck these days.

Having said that however, RAID *IS* a great way to squeeze performace
out of older hardware for file storage and sharing purposes.
Distributing reads/writes through a raid controller enables utilization
of that maximum bandwidth, which would not otherwise be possible through
a single drive - even newer drives.

Paul

> -----Original Message-----
> From: fedora-list-bounces at redhat.com 
> [mailto:fedora-list-bounces at redhat.com] On Behalf Of James Wilkinson
> Sent: Monday, December 06, 2004 6:35 AM
> To: For users of Fedora Core releases
> Subject: Re: IDE controller card and Fedora Core 3
> 
> Robert L Cochran wrote:
> > You want to RAID5 640 Gb  worth of drives on a Pentium II, 400 MHz 
> > machine? I'm not a RAID expert. I question whether doing it 
> on an old, 
> > slow machine with large drives is practical. It seems to me 
> you would 
> > simply saturate the PCI bus.
> 
> Depends. (And I know the Original Poster later said performance wasn't
> critical...)
> 
> Firstly, unlike certain OSes, Linux should find that a 
> Pentium II is fine for shoving data around. It's not like it 
> needs to do complex calculations on each byte: it shouldn't 
> even need to examine each byte while reading.
> 
> Of course, while it's writing, something will have to calculate
> checksums: I don't think the Original Poster's suggested card 
> has any RAID acceleration features.
> 
> Secondly, it depends exactly what you're going to put on that 
> RAID array. If you're putting a mail server or a database on 
> it, you'll almost certainly find that disk usage is dominated 
> by lots and lots of small (~8K) reads. And you'll be very 
> lucky to get more than about 150 of those per second on ATA drives. 
> 
> It's all about physics: on a hard disk that spins about 100 
> times per second, a particular byte only goes near the read 
> heads once every 10 ms. And no matter how fast the rest of 
> the computer is, 10 ms is an age in computing. Database 
> administrators swear by the "number of spindles", for this 
> reason: I've got much chunkier disk arrays on not much faster 
> systems. (They also swear *at* RAID 5 for a lot of usages...)
> 
> And 8K times 150 transfers per second = 1200 K/s per disk: 
> that's not going to set anything on fire.
> 
> (The Original Poster mentioned SAMBA, but it still depends on 
> what sort of files are being stored).
> 
> Thirdly, on a slow PCI implementation, you're going to get 90 
> - 100 MB/s of usable bandwidth. Hard drives are only just 
> going past the 70 MB/s at peak performance. At the best of 
> times, you are going to be limited by the PCI bus, but you're 
> still going to get better than a single drive on the latest systems.
> 
> Of course, on a Samba server, you're going to be sharing that 
> bandwidth with the network card (on a PII 400). If that's 
> gigabit, then yes, that's going to halve the available 
> bandwidth and slow things down. If it's only 100 Mbit/s, then 
> that's 12.5 MB/s max, and that's your
> bottleneck: that's the physical maximum you'll get out of the system.
> 
> (When did 100 Mbit/s become "only"?)
> 
> But this is why PCI Express is a Good Thing. It's designed 
> for this sort of job: a separate network card and a separate 
> fast hard drive adapter.
> The bandwidth isn't shared: they each get their own 2.5 
> Gbit/s per lane in each direction.  Although you might 
> *still* need more than 1x PCIe for the hard drive adapter...
> 
> James.
> -- 
> E-mail address: james | Anonymous:          What do you think 
> of Stainer's
> @westexe.demon.co.uk  |                     "Crucifixion"?
>                       | Sir Thomas Beecham: Good idea! 
> 
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