Date: Tue, 18 Apr 2017 01:49:46 +0200 From: Polytropon <freebsd@edvax.de> To: Manish Jain <bourne.identity@hotmail.com> Cc: "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org> Subject: Re: Is it possible to install FreeBSD on a single MBR slice with ZFS ? Message-ID: <20170418014946.fa114b49.freebsd@edvax.de> In-Reply-To: <VI1PR02MB120024156110981D6A3B4C80F6060@VI1PR02MB1200.eurprd02.prod.outlook.com> References: <VI1PR02MB12004B1D8A87B3E247FC1A66F6040@VI1PR02MB1200.eurprd02.prod.outlook.com> <e2f76fb0-05e0-5a53-1730-a5a64291c407@holgerdanske.com> <VI1PR02MB120024156110981D6A3B4C80F6060@VI1PR02MB1200.eurprd02.prod.outlook.com>
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On Mon, 17 Apr 2017 13:45:25 +0000, Manish Jain wrote: > >>AFAIK, the FreeBSD 11.0 installer wants the whole disk << > > Hi David, > > That appears to be my impression too : it simply is not possible > to install FreeBSD on an MBR disk > (unless one is willing to use the entire disk). That's not correct. If you go with MBR, you usually need _one_ slice unoccupied. This is where you install FreeBSD partitions to (which then carry the file systems or act as swap space). Example: ada0 = the whole disk ada0s1 = 1st slice, contains some "Windows" ada0s2 = 2nd slice, contains maybe DOS ada0s3 = 3rd slice, contains FreeBSD ada0s3a = FreeBSD / file system ada0s3b = FreeBSD swap space ada0s3[d-h] = some more FreeBSD file system ada0s4 = 4th slice, still empty This example of course applies to UFS. If you use ZFS, it should be possible to give ada0s3 to FreeBSD ZFS, but of course there would not be any BSD partitions inside. > That is a fairly serious inconvenience : I hate the idea of having > to use GPT on my disk because I cannot use the Boot Easy manager > (boot0cfg) under GPT. Plus GPT inevitably leads to reckless > partitioning. Do not confuse MBR and GPT. Both can be used for "whole disk as a whole" or "many small partitions". But you are right that there may be situations where multiboot-environments require specific hacks to get working. For comparison, check this article: http://www.wonkity.com/~wblock/docs/html/disksetup.html > For disks under and upto 2 TB, MBR is supremely better. Or GPT - it actually does not matter. Today, GPT is advised unless you have a good and valid reason to use MBR. Or you use _none_ of them, no GPT, no MBR. This approach is called "dedicated" and does not involve any disk partitioning, only BSD partitions (ada0[a-h] to follow the example provided above). This of course is not really a good idea for multiboot environments. > I did manage to get ZFS though, courtesy a spare slice available > on my disk. That is a fully valid approach. > I installed FreeBSD using UFS on ada0s2 and migrated the setup > to a ZFS tank under ada0s3 using the rsync strategy > brilliantly detailed at : > > https://imil.net/blog/2016/04/28/Migrate-FreeBSD-root-on-UFS-to-ZFS/ That "UFS to ZFS" approach is also possible if you can't (or don't want to) install ZFS right from the start. > But following the migration, I have made a serious error. I used > Windows (ada0s1) to delete ada0s2 : > Windows has rearranged the MBR table to make ada0s3 -> ada0s2. Sounds like something OS/2 has done to me many years ago. :-) > I am now struggling to fix the MBR table. Of course. > If you have any tips, that shall be wonderful Do not and never use "Windows" to deal with lower level aspects of your disk. It will for sure mess things up, and in worst case, you need to reinstall everything from scratch. Of course you don't, as you have a working backup you can rely on. ;-) It's not as easy anymore to fix partition table entries with a simple handheld calculator and "Norton Disk Editor" started from a handy DOS boot floppy. :-) For the future: Bootable CDs like UBCD or PartEd Magic provice excellent tools to deal with re-partitioning. You can use FreeBSD's editor as well, especially if all you want to do is delete some MBR slices. It's the first thing you do in the installer, then follow to create new slices as you need them, and go on with the installation process. -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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