[OmniOS-discuss] LTS r151014 installation issue from USB stick

[Peter Tribble]

On Sat, Aug 13, 2016 at 12:36 PM, Michael Mounteney <gate03 at landcroft.co.uk>
wrote:

> On Sat, 13 Aug 2016 12:59:52 +0200
> Krzysztof Grzempa <grzempek at gmail.com> wrote:
>
> > Correct me if I'm wrong..There is no way to setup raidz on rpool.
> > Right ?
>
> In the simple case, that's so because when you first boot the computer,
> the BIOS or boot firmware (of whatever type) has to read boot data of
> some sort; either a boot loader (GRUB/LILO on x86, LILO on others) or
> the kernel itself directly.
>
> On a raidz system, the data are spread across all disks and don't exist
> in entirety on any one disk.  So unless the firmware can read from
> multiple disks and re-assemble the boot loader or kernel, it can't boot
> the OS.  Since raidz can be in a variety of configurations, it would be
> very hard to give the firmware the necessary information.
>

Not exactly. The firmware reads the bootloader, currently in our case grub.
The bootloader isn't accessed through the filesystem at all, so you could in
theory put grub onto the disks in a raidz pool and the firmware would read
it
just fine.

However, grub has a fairly rudimentary understanding of zfs, as it has its
own
implementation of a basic zfs reader:


https://github.com/illumos/illumos-gate/blob/master/usr/src/grub/grub-0.97/stage2/fsys_zfs.c

This can basically walk a single disk. Which allows mirrors (because the
other
disks are the same), but anything beyond that won't work. So no log devices,
no stripes, no raidz.

It's not a fundamental architectural limitation, just that the actual grub
implementation only covers the simplest possible case.

-- 
-Peter Tribble
http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/
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