Date: Sun, 17 Jan 2010 16:39:41 +0000 From: Mike Clarke <jmc-freebsd2@milibyte.co.uk> To: freebsd-questions@freebsd.org Cc: Pieter de Goeje <pieter@degoeje.nl> Subject: Re: Newbie gmirror questions Message-ID: <201001171639.41777.jmc-freebsd2@milibyte.co.uk> In-Reply-To: <201001161545.31616.pieter@degoeje.nl> References: <201001152334.52978.jmc-freebsd2@milibyte.co.uk> <201001161545.31616.pieter@degoeje.nl>
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On Saturday 16 January 2010, Pieter de Goeje wrote: > On Saturday 16 January 2010 00:34:52 Mike Clarke wrote: > > I'm about to upgrade to more disk space and I'm tempted use this as > > an opportunity to get two disks and implement gmirror. Before I go > > ahead there's a few aspects of mirroring I'm not sure about and > > would appreciate some advice. > > > > I'm using grub for multi booting. Does this introduce any problems > > if I want to boot into Windows or Linux on one of the other > > partitions? > > Gmirror stores the metadata at the last sector of each disk. So this > shouldn't be a problem. But other operating systems might overwrite > this data if you're not careful during the paritioning. I'll make sure that the last stripe on the disk isn't used by any "alien" OS then. Actually I was more concerned about what happens when I boot into another OS like Windows or Linux on one of the spare slices - I'm assuming that I have to apply gmirror to the whole disk rather than just selected slices? My main reason for multibooting with grub is to have a spare slice where I can install a spare copy of FreeBSD. I find this very useful when I do any major upgrade (like trying out your suggestion of going to 8-STABLE) because I can copy the current system onto the spare slice and use that to apply the upgrades, if I hit any major problems I can easily revert to booting the original slice until I figure out how to fix the problem. I'm assuming that using gmirror won't prevent me from doing this. If I boot into an OS which isn't aware of gmirror, such as Windows, then I assume it will just run normally if I point grub to the appropriate slice on the primary drive. Next time I boot into FreeBSD then I expect gmirror will recognise that the second drive is out of sync with the primary and update it in the background. Perhaps this might hit performance for a while but on the other hand it provides me with a certain amount of "backup" if the Windows system trashes itself because I could try to restore it from the copy on the second drive before attempting to reboot FreeBSD. I assume the same logic would also apply to running Linux on one of the slices, although Linux has software mirror capability it appears to be totally different from gmirror so I expect it's a case of running that non-mirrored too. If this approach isn't wise then I expect I'll need to keep a spare non-mirrored disk for the other systems. I don't expect to need to boot into Windows or Linux very often. Now that I've upgraded from FreeBSD 6.4 to 8.0 I'm able to make use of virtualbox for this sort of thing which is generally much more convenient but I'd like to keep the ability to run them natively should the need arise. -- Mike Clarke
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