Date: Fri, 9 Feb 2007 14:41:39 -0600 From: Josh Paetzel <josh@tcbug.org> To: freebsd-stable@freebsd.org Cc: Artem Kuchin <matrix@itlegion.ru> Subject: Re: What is a good choice of sata-ii raid controller for freebsd? Message-ID: <200702091441.39848.josh@tcbug.org> In-Reply-To: <01e601c74c5d$31be19c0$0c00a8c0@Artem> References: <00ad01c74b65$79db1710$0c00a8c0@Artem> <45CC72D4.9040104@lxnt.info> <01e601c74c5d$31be19c0$0c00a8c0@Artem>
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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. =20 If a drive in the mirror fails the device name available to the OS is=20 still the same. The FreeBSD loader does not do gmirror, it boots off=20 the raw device, and then gmirror is loaded. If the drive you are=20 booting off of fails you have to have the BIOS set to boot from the=20 other drive in the mirror, and then you run into 'what is the root=20 device set to in loader.conf' issues. =46rom a raw speed perspective on an unloaded CPU a 3.0ghz processor is=20 probably just as fast or faster than the embedded processor on a RAID=20 card running at a few hundred mhz. Sure, once you start talking=20 about CPUs at full load there are advantages to off-loading stuff to=20 a dedicated processor. =2D-=20 Thanks, Josh Paetzel
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