Re: A further question on my "how to move to an NVME disk" question

[Chris Green]

On Thu, Nov 21, 2019 at 09:27:48PM +0000, Chris Green wrote:
> On Thu, Nov 21, 2019 at 09:51:03PM +0100, Pascal Hambourg wrote:
> > Le 21/11/2019 à 20:46, Chris Green a écrit :
> > > 
> > > However trying to boot 19.10 from /dev/nvme0n1p2 fails with "No such
> > > device c6ca1c2d-4837-48b9-8fa6-1ef47251d7b7" whereas booting it from
> > > /dev/sda1 (a spare SATA spinning disk) boots OK.  The device UUID is
> > > correct for /dev/nvme0n1p2 so I guess grub isn't able to read the NVME
> > > SSD for some reason.
> > 
> > Of course. GRUB uses the BIOS for disk access, but the BIOS cannot manage
> > the NVMe SSD.
> > 
> > >  How do I get over *this* issue! :-)
> > 
> > As explained before : you must put Ubuntu 19.10's /boot in a location which
> > the BIOS can see, such as the SATA SSD. But DO NOT share the same /boot
> > between both Ubuntu's, else GRUB won't be able to tell which kernels belong
> > to which system.
> > 
> OK, yes, I see.  So I need to put the /boot for /dev/nvme0n1p2 on
> /dev/sda1 or similar.  How does one configure that though?  I.e. if I
> clear out my 'spare' /dev/sda1 and just put a /boot on it how do I
> tell update-grub to configure grub so that the /boot is on /dev/sda1
> but the rest of the OS is on /dev/nvme0n1p2?
> 
...  or even better can I configure things so that there are two
different 'boot' directories (with different names) on my (fairly)
fast SATA SSD /dev/sdb1r?  One would be for the xubuntu 19.04 system
(which has its files on the SATA SSD /dev/sdb1) and one for the
xubuntu 19.10 system which has its files on /dev/nvme0n1p2.

I.e. does grub insist on its configuration/files being in a directory
called /boot?  

Further to this I suppose I can create a small new partition on the
'relatively fast' SATA SSD in which I create the /boot for the new
19.10 installation on /dev/nvme0n1p2.  This wouldn't be an issue.

So, I *think* the resulting configuration would be:-

    /dev/sda - unused, spare spinning disk

    /dev/sdb
        /dev/sdb1 - Linux partition with /boot and the rest of 19.04 
installation
        /dev/sdb2 - Small partition with /boot for 19.10 whose files are on 
/dev/nvme0n1p2

    /dev/sdc
        /dev/sdc1 - /home

    /dev/nvme0n1
        /dev/nvme0n1p1 - swap
        /dev/nvme0n1p2 - 19.10 installation (but no /boot)


... but I still don't quite know how to tell 
grub-mkconfig/grub-install/update-grub
how to make things like this.

-- 
Chris Green