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Re: [zfs-discuss] ZFS Mountroot and Bootroot Comparison

Subject: Re: [zfs-discuss] ZFS Mountroot and Bootroot Comparison
From: Eric Schrock
Date: Thu, 4 Oct 2007 10:02:41 -0700
Remember that you have to maintain an entirely separate slice with yet
another boot environment.  This causes huge amounts of complexity in
terms of live upgrade, multiple BE management, etc.  The old mountroot
solution was useful for mounting ZFS root, but completely unmaintainable
from an installation and upgrade perspective.  It was dropped because we
could not possibly develop installation, packaging, and upgrade software
that would work across multiple BEs under such a scheme.

- Eric

On Thu, Oct 04, 2007 at 11:27:46PM +0700, Kugutsumen wrote:
> Lori Alt told me that mountrount was a temporary hack until grub  
> could boot zfs natively.
> Since build 62, mountroot support was dropped and I am not convinced  
> that this is a mistake.
> 
> Let's compare the two:
> 
> Mountroot:
> 
> Pros:
>    * can have root partition on raid-z: YES
>    * can have root partition on zfs stripping mirror: YES
>    * can have usr partition on separate ZFS partition with build <  
> 72 : YES
>    * can snapshot and rollback root partition: YES
>    * can use copies on root partition on a single root disk (e.g. a  
> laptop ): YES
>    * can use compression on root partition: YES
> Cons:
>    * grub native support: NO (if you use raid-z or stripping mirror,  
> you will need to have a small UFS partition
>      to bootstrap the system, but you can use a small usb stick for  
> that purpose.)
> 
> New and "improved" *sigh* bootroot scheme:
> 
> Pros:
>    * grub native support: YES
> Cons:
>    * can have root partition on raid-z: NO
>    * can have root partition on zfs stripping mirror: NO
>    * can use copies on root partition on a single root disk (e.g. a  
> laptop ): NO
>    * can have usr partition on separate ZFS partition with build <  
> 72 : NO
>    * can snapshot and rollback root partition: NO
>    * can use compression on root partition: NO
> 
> Why did we completely drop support for the old mountroot approach  
> which is so much more flexible?

--
Eric Schrock, Solaris Kernel Development       http://blogs.sun.com/eschrock
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