Mailinglist Archive: opensuse (5130 mails)

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Re: DMA, ATA standards, etc... -- WAS: Advantages of Dual Core
  • From: "Bryan J. Smith" <b.j.smith@xxxxxxxx>
  • Date: Sun, 28 May 2006 08:25:13 -0400
  • Message-id: <1148819113.2724.62.camel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Anders Johansson:
> Compare with viewing DVDs, for example. With DMA, you can view a DVD
> on a relatively low end system. Without it, you get stuttering on
> even very good systems

Software RAID-5 writes are essentially PIO. And the worst thing about
it is that you won't see the bottleneck in CPU load or even CPU I/O
serving. But it essentially brings any desktop system down to 20-30MBps
during writes.

Orn E. Hansen wrote:
> It's a SATA drive ... haven't seen any DMA settings for that yet.

Per Jessen wrote:
> I'm not sure, but I suspect the SATA interface chips use only DMA. I
> see no reason why the SATA standard would include PIO support or any
> such ancient stuff.

SATA is DMA-only. That's one of the reasons why you can only have 1
device per channel.

Now also remember that there is ATA (simple block -- e.g., hard drive)
and then ATAPI (rich block command set -- e.g., optical) -- ATAPI is a
_super_set of ATA. SATA ATAPI devices are very _problematic_ right now,
because most are using ATA-to-SATA converters. The result is not only
do many SATA drivers lack support for the full ATAPI command set, but
sometimes these ATAPI devices slip into PIO mode.

That's why most SATA ATAPI devices only work on select ATA controllers
-- like the Intel ICH6+.

Bryan J. Smith Professional, technical annoyance
Americans don't get upset because citizens in some foreign
nations can burn the American flag -- Americans get upset
because citizens in those same nations can't burn their own

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