Date: Wed, 23 Jun 2004 17:32:31 +0200 From: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos@DeepCore.dk> To: Maxim Sobolev <sobomax@portaone.com> Cc: Eric Veraart <eric@monkey-online.net> Subject: Re: HostRaid support on FreeBSD Message-ID: <40D9A28F.6020602@DeepCore.dk> In-Reply-To: <40D99F19.5010008@portaone.com> References: <5.2.1.1.0.20040621135534.068fef40@server01.chassis00.xsnetworks.net> <40D7E0B7.1000905@portaone.com> <40D8D217.5000808@freebsd.org> <40D95FDC.9060802@portaone.com> <40D99D3B.8010608@DeepCore.dk> <40D99F19.5010008@portaone.com>
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Maxim Sobolev wrote: > Søren Schmidt wrote: > >> Maxim Sobolev wrote: >> >>> Well, my knowelege about internals of software RAID controllers is >>> quite limited, but as long as I know they are no more than BIOS with >>> UI for setting up RAIDs and interface to main BIOS that hides >>> internal RAID structure allowing to boot off the RAID. Also they >>> provide some persistent storage for RAID configuration, I assume >>> either in some controller's NVRAM or on the HDDs. Therefore, the same >>> set of GEOM RAID modules can work with different software RAID >>> controllers (SCSI, ATA, SATA etc) if there will be a standard way to >>> extract this info from the controller's driver, and present it in >>> some common format. That's what I am talking about. >> >> >> >> Well, I dont know about SCSI, but ATA/SATA always stores the metadata >> on disk, the controller has nothing todo with the RAID functionality, >> its merely a way to talk to the disks. >> >> Reading the metadata off the disks and using that info to access a >> RAID array is easy and can be had even without docs in a few hours. >> Writing back the metadata in case of failures etc to retain sanity of >> the array is "somewhat" more difficult. Actually I'm working with this >> currently for new formats for ata-raid and its not trivial to get right. > > > But I assume that on-disk format of this info and its location is > controller-dependent, so that appropriate code to read/decode this info > should probably be in the controller's driver. Not exactly, its BIOS vendor depended, I know of at least a handfull of controller chips that can be had with at least 2 different BIOS software RAID's that uses different metadata. In some cases you can even take a stack of disks thats normally on a HW RAID controller (like the promise sx6000) and use it on a software RAID setup as the metadata is the same and known by ata-raid. At any rate, this isn't as simple as it sounds (as usual) :) -- -Søren
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