FreeBSD 5.3b7and poor ata performance
cswiger at mac.com
Mon Oct 25 13:39:30 PDT 2004
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
> with it.
Oh, I'm not trying to throw stones your way, or at GEOM, or anywhere
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
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".
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