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Date:      Thu, 22 Mar 2018 07:28:14 -0600 (MDT)
From:      Warren Block <wblock@wonkity.com>
To:        Victor Sudakov <vas@mpeks.tomsk.su>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Solved. Re: Dualboot and ZFS
Message-ID:  <alpine.BSF.2.21.1803220726210.5586@wonkity.com>
In-Reply-To: <20180322012621.GA15678@admin.sibptus.transneft.ru>
References:  <VI1PR02MB1200C7F0066F361E60A6CBEDF6EB0@VI1PR02MB1200.eurprd02.prod.outlook.com> <20180115144747.GA65526@admin.sibptus.transneft.ru> <VI1PR02MB120018D174817F8FFB2981D5F6EB0@VI1PR02MB1200.eurprd02.prod.outlook.com> <20180115151526.GA66342@admin.sibptus.transneft.ru> <a7920f859b666cff48f4f73ee1b2f954@dweimer.net> <20180116034929.GB89443@admin.sibptus.transneft.ru> <20180131082738.GA46395@admin.sibptus.transneft.ru> <547e65d16ef16667f61d88463ca73079@roundcube.fjl.org.uk> <20180319025914.GA57490@admin.sibptus.transneft.ru> <alpine.BSF.2.21.1803210626040.85475@wonkity.com> <20180322012621.GA15678@admin.sibptus.transneft.ru>

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On Thu, 22 Mar 2018, Victor Sudakov wrote:

> Warren Block wrote:
>> On Mon, 19 Mar 2018, Victor Sudakov wrote:
>>>
>>> sysctl kern.geom.debugflags=0x10
>>
>> Please reconsider doing this without it being required.  It means "allow
>> destroying mounted partitions" and is usually not necessary.
>
> It is recommended, or even required ("must") by the zfsboot(8) man page:

The vagueness here is from the "If the drive is currently in use".  It 
could easily be replaced with "If the user wants to destroy data from a 
drive that is currently being used".  I would argue that we should 
remove or rewrite that, as it is misleading.  Overwriting a drive that 
is "in use" is generally exactly the opposite of what people want.

> EXAMPLES
>     zfsboot is typically installed using dd(1).  To install zfsboot on the
>     ada0 drive:
>
>           dd if=/boot/zfsboot of=/dev/ada0 count=1
>           dd if=/boot/zfsboot of=/dev/ada0 iseek=1 oseek=1024
>
>     If the drive is currently in use, the GEOM safety will prevent writes and
>     must be disabled before running the above commands:
>
>           sysctl kern.geom.debugflags=0x10
>
>     zfsboot can also be installed in an MBR slice:
>
>           gpart create -s mbr ada0
>           gpart add -t freebsd ada0
>           gpart create -s BSD ada0s1
>           gpart bootcode -b /boot/boot0 ada0
>           gpart set -a active -i 1 ada0
>           dd if=/boot/zfsboot of=/dev/ada0s1 count=1
>           dd if=/boot/zfsboot of=/dev/ada0s1 iseek=1 oseek=1024
>
>
>
>



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