Date: Thu, 21 Jul 2005 15:03:10 +0200 From: Stijn Hoop <stijn@win.tue.nl> To: Norberto Meijome <freebsd@meijome.net> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: Bootstrapping Raid 5 w/GEOM Message-ID: <20050721130310.GY72402@pcwin002.win.tue.nl> In-Reply-To: <42DF9B87.2000708@meijome.net> References: <42DF4A96.1080305@meijome.net> <20050721124049.GX72402@pcwin002.win.tue.nl> <42DF9B87.2000708@meijome.net>
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On Thu, Jul 21, 2005 at 10:56:39PM +1000, Norberto Meijome wrote: > Stijn Hoop wrote: > > On Thu, Jul 21, 2005 at 05:11:18PM +1000, Norberto Meijome wrote: > > > I want to setup software Raid 5 , and I want it to affect ALL > > > partitions, including / (so if any one of the drives fails, it will > > > still boot up properly). I am planning on using GEOM, but open to > > > suggestions. > > > > I don't think it's possible -- the loader doesn't know about the mirror > > even in a mirrored / setup; it justs treats one of the disks of the mirror > > as 'the boot disk'. It's not until the kernel is loaded that gvinum RAID-5 > > can do something. > > Would the same be true (not possible to boot) for a RAID 1 + 0 with GEOM? Hmm, tricky. I guess if you can get the disk layout to mirror that of a non-RAID one, the loader would be able to cope. Striping would be impossible (at least not unless you can guarantee that the whole of the kernel + / and /boot directory entries are available on one stripe, and even then I'm not sure). > > So, in your case, the loader would read random RAID-5 data instead of > > a kernel and refuse to boot. > > > > IE, it's not possible until someone writes a RAID-5 capable loader. > > right - so that's why I couldnt find any reference to this anywhere :) Probably. > > I would advise you to either use gmirror for booting, or define a few > > gvinum mirror plexes (it is possible to boot from a mirrored gvinum > > setup although it's tricky to get right). > > I guess I could create a boot slice in 2 of the drives, mirror that with > gmirror and use that to boot. Then RAID-5 the rest of the drives (minus > the size of the boot partition in the other 2 drives of course). Yes. While on the subject, you could use 2 drives to mirror the boot disk and have swap, and then use the same amount of space on the other two drives to mirror /usr and /var. Then use RAID-5 for your data partitions. This way you'll have speed & reliability. Be aware that RAID-5 is not ideal for many-write situations (most home directories), although certainly tolerable with modern drives. --Stijn -- I wish there was a knob on the TV to turn up the intelligence. There's a knob called `brightness', but it doesn't work." -- Gallagher
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