Date: Mon, 26 Feb 2007 12:11:32 +0100 From: Fluffles <etc@fluffles.net> To: Paul van der Linden <msn@paultjuh.org> Cc: freebsd-hardware@freebsd.org Subject: Re: Hardware supported? Message-ID: <45E2C064.3060704@fluffles.net> In-Reply-To: <45E2B60F.9030108@paultjuh.org> References: <45E1DA61.8090607@paultjuh.org> <45E2224B.9030605@fluffles.net> <45E2B60F.9030108@paultjuh.org>
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Paul van der Linden wrote: > Fluffles wrote: >> Onboard RAID does not really exist. The actual RAID is done by drivers; >> onboard RAID is actually software RAID with a minor RAID BIOS which can >> write metainformation about the array configuration and has BIOS >> bootstrap support. This is also called "fake RAID". FreeBSD does support >> some fake RAID metainformation though, by reading the metainfo from the >> disks and assigning it's own software RAID-mechanism to it. For >> information of which metainformation formats are supported, checkout the >> ataraid(4) manpage: >> http://www.freebsd.org/cgi/man.cgi?query=ataraid&apropos=0&sektion=4&manpath=FreeBSD+6.2-RELEASE&format=html >> >> > > Thank you, what are the disadvantages of a fake RAID? No hardware acceleration and you are bound to the motherboard or similar chipset with RAID controller. So if your motherboard dies, you cannot just use another motherboard, since this motherboard will likely have another chipset which uses another metadata structure. Thus, you will have trouble getting your data back if you are unexperienced. The only thing fake RAID does implement is proper boot support; if that is not required then i strongly advise you to use software RAID (gstripe) instead; to be more flexible and hardware-independent. > I was planning to setup my server with raid 1, But will it still boot > when 1 harddisk fails? Yes, this will actually work with both fake RAID (onboard RAID) and software RAID. Because with RAID1, you can boot off both disks, or the logically created array. Once booted, FreeBSD should identify the RAID volume and act appropriately. If one disk is missing, it will not update it, so you will be running in a degraded mode. If ataraid(4) does not support writing metadata for the fake RAID controller, you will have to reboot and 'rebuild' your volume in the controller BIOS. This is of course more troublesome then with software RAID. If FreeBSD supports writing the metadata format, however, no reboot is necessary and you can rebuild with atacontrol(4). - Veronica
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