Date: Wed, 23 Jun 2004 18:17:45 +0300 From: Maxim Sobolev <sobomax@portaone.com> To: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos@DeepCore.dk> Cc: Eric Veraart <eric@monkey-online.net> Subject: Re: HostRaid support on FreeBSD Message-ID: <40D99F19.5010008@portaone.com> In-Reply-To: <40D99D3B.8010608@DeepCore.dk> 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>
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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. -Maxim
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