From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brad Campbell Subject: Re: Benchmarks: Linux Kernel RAID vs a Hardware RAID setup Date: Wed, 23 Jul 2008 14:29:37 +0400 Message-ID: <48870811.8050402@wasp.net.au> References: <1216130769.5633.318.camel@sam.localdomain> <20080715163932.GA23164@rap.rap.dk> <487CEF1A.6050402@wasp.net.au> <20080715201221.GB26439@rap.rap.dk> <4884BF7B.6030206@tmr.com> <20080723074539.GA13549@rap.rap.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20080723074539.GA13549@rap.rap.dk> Sender: linux-raid-owner@vger.kernel.org To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= Cc: Bill Davidsen , Ben Martin , linux-raid@vger.kernel.org List-Id: linux-raid.ids Keld J=F8rn Simonsen wrote: >>> It is possible that I am thinking of what you call fakeraid. >>> =20 >> I like "firmware raid" better, but the bottom line here is that the = raid=20 >> is still done in the system CPU. These often have little or no hardw= are=20 >> support, such as cache so that multiple drives can be written withou= t=20 >> passing the data through the system bus more than once (and chancing= =20 >> change while that happens). >=20 > OK, if the definition on these controllers is that they must have sup= port > from the OS, then I think most of the mobos today come with hardware > raid, that is there needs to be no support in Linux for this. Everyth= ing > is set up via the bios, and from the linux kernel it looks like an > ordinary disk. The problem here is it looks like an ordinary disk to the BIOS only. Gr= ub can use this to load the=20 kernel and initrd from, but when the kernel boots it sees the controlle= r as the simple controller it=20 is with some disks connected to it. It requires something like dmraid t= o make the "array" visible as=20 an actual array. None of these controllers perform any of the RAID offload themselves, i= t's all handled by the=20 driver. Windows loads using the BIOS and then hands over to the driver = which handles the raid, just=20 the same as linux does with dmraid. I believe some of the ITE chipsets can handle raid-1 and possibly raid-= 0 internally, and the kernel=20 has the ability to drive those as a raid controller, but they are somew= hat rarer than the other=20 fakeraid implementations out there. Brad --=20 Dolphins are so intelligent that within a few weeks they can train Americans to stand at the edge of the pool and throw them fish. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html