Date: Thu, 3 Jan 2008 09:25:27 -1000 From: Clifton Royston <cliftonr@lava.net> To: "Chris H." <chris#@1command.com> Cc: freebsd-stable@freebsd.org Subject: Re: gmirror on 7B4 Message-ID: <20080103192526.GA18773@lava.net> In-Reply-To: <20080102084743.xtecj951wogwws8w@webmail.1command.com> References: <20080102002651.r72jwx0pgk4000c8@webmail.1command.com> <20080102070518.ki0v7vxkgo0cossg@webmail.1command.com> <20080102111751.5huybrwosgs0ccos@newwebmail.jnielsen.net> <20080102112230.g7p1bj3sdck488g8@newwebmail.jnielsen.net> <20080102084743.xtecj951wogwws8w@webmail.1command.com>
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On Wed, Jan 02, 2008 at 08:47:43AM -0800, Chris H. wrote: > Quoting John Nielsen <lists@jnielsen.net>: > > >I'm not sure I remember everything from earlier in this thread so I > >don't know if it's relevant, BUT you can't boot from a gstripe volume > >(or from a gconcat one AFAIK). Inferring from your fstab example > >below it doesn't sound like you intend to but I just wanted to be > >sure. > > Are you sure? I read that using gmirror requires /kernel to be located > in the /boot slice and everything else (all other slices) can be mirrored > safely. But in all my reading (man pages, FBSD handbook, asstd articles) > I haven't seen anything indicating booting wasn't possible from a gstripe > volume. Your current idea is backwards; you can boot from entirely mirrored drives (i.e. RAID1) and I've been doing it since 5.3, but AFAIK it is impossible to boot from a striped drive and I suspect will remain so for a long time. One way to visualize this is to recognize that because the gmirror information is stored at the very end of the lower-level GEOM object, each of the raw drives in the mirrored set appears to be an perfectly normal drive when reading it from its beginning; thus it is possible to simply read it as a normal device during the earlier stages of boot until GEOM and gmirror loads. With striping, however, the logical content is spread out across multiple drives, so any one drive you try to boot from has only 1/Nth of the relevant sectors. Does this help? -- Clifton -- Clifton Royston -- cliftonr@iandicomputing.com / cliftonr@lava.net President - I and I Computing * http://www.iandicomputing.com/ Custom programming, network design, systems and network consulting services
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