What is a good choice of sata-ii raid controller for freebsd?

Josh Paetzel josh at tcbug.org
Fri Feb 9 20:41:52 UTC 2007

On Friday 09 February 2007 09:15, Artem Kuchin wrote:
> Alexander Sabourenkov wrote:
> > Artem Kuchin wrote:
> >> hi!
> >>
> >> I am the original poster of this thread. I have read many
> >> interesting reply during these two days. However, as i said in
> >> the original message due to certification issues i am pretty
> >> limited to INTEL controllers  and i have not seen a single
> >> relevant reply about them. This is interesting. Nobody uses
> >> Intel controllers on FreeBSD or they just suck that much?
> >
> > If you have enough  SATA ports and no need for fancy RAID levels,
> > then my advice is to use gmirror.
> >
> > Hardware RAID1 buys you nothing in perfomance and reliability
> > for a prolonged headache with drivers, bios insanity and
> > monitoring+control tools.
> Hm... two points here. I, somehow, do not really believe that
> software raid (gmirror for example) is as reliable as hardware.
> I, deeply inside, believe that i might screw things very badly
> under some heavy load and bad timing conditions. Can't explain it.
> it is religious i guess, but i can be very wrong about this.
> However, two perfomance point:
> Under gmirror OS must issue two commands to write to disks and some
> commands to check/set mark that mirrored data is intact.
> Under hardware RAID OS issue sonly one command to write and no
> checking command, since raid controller handles this async.
> So, software OS raid must be slower than controller based raid
> anyway.
> Am i right here? Any benchmark data on this?
> As for reliability of gmirror. I just need to know how it works to
> see for myself that if power turned off in some racing condition
> gmirror will know that disk are out of sync. If it is done than
> gmirror must check sync of disks every read, and that mean two
> command for reading too, which must slow down things. Is it true?
> --
> Artem

What hardware RAID buys you over gmirror is that you can boot from it.  
If a drive in the mirror fails the device name available to the OS is 
still the same.  The FreeBSD loader does not do gmirror, it boots off 
the raw device, and then gmirror is loaded.  If the drive you are 
booting off of fails you have to have the BIOS set to boot from the 
other drive in the mirror, and then you run into 'what is the root 
device set to in loader.conf' issues.

From a raw speed perspective on an unloaded CPU a 3.0ghz processor is 
probably just as fast or faster than the embedded processor on a RAID 
card running at a few hundred mhz.  Sure, once you start talking 
about CPUs at full load there are advantages to off-loading stuff to 
a dedicated processor.


Josh Paetzel

More information about the freebsd-stable mailing list