Re: FreeBSD 5.3b7and poor ata performance

On Oct 25, 2004, at 3:49 PM, Scott Long wrote:
[ ... ]
>> Your position is certainly reasonable: if a storage system is not 
>> reliable, how fast it performs is something of a moot point.  :-)  
>> However, this being said, a RAID-0 implementation needs to improve 
>> performance compared with using a bare drive if it is to be useful.
>
> Well, RAID-0 is a special case =-)

Sort of, yeah.  It's hard to make generalizations about RAID 
performance without considering each mode as a separate case...in which 
case, your generalizations aren't very general.  8-)

> That said, putting discrete RAID
> classes into the GEOM layer is something of a new adventure, so I'm
> not surprised to hear about performance problems, even in RAID-0.
> There might be extra data copies or path latencies that weren't planned
> for or expected.  It's definitely something to look at.  But it's also
> a very new subsystem, so it would be unfair to judge FreeBSD 
> performance
> with it.

Oh, I'm not trying to throw stones your way, or at GEOM, or anywhere 
else.

By and large, you would be right to claim that RAID generally performs 
less well than direct access to bare drives.  This conclusion is driven 
as much by how frequently RAID-5 gets used compared with the 
less-common RAID modes as anything else, however.  Someone who uses 
RAID-0 or RAID-1,0 modes really does expect to see a performance 
improvement.

-- 
-Chuck

PS: And yes, I know that talking about how something should perform 
doesn't get code written, but it can be helpful to recognize that 
system ought to function at a certain level in order to be "useful".