Re: grub-install problem after trixie upgrade
On Mon, Aug 11, 2025 at 01:36:03AM +0100, Alain Williams wrote:
> I get an error installing grub. I do not understand it let alone know how to
> fix it. Note that the error happens for sda but not sdb:
> grub-install: warning: You have a short MBR gap and use advanced config. Please increase post-MBR gap..
> grub-install: warning: your core.img is unusually large. It won't fit in the embedding area.
> grub-install: error: embedding is not possible, but this is required for RAID and LVM install.
I have a clue ... If I run on the 2 disks "fdisk -l" I see a difference in
layout that I had not noticed before. The start of partition 1 is not in the
same place. On sda it is at 64 (not 2048) which might be the "short MBR gap":
sda:
Device Boot Start End Sectors Size Id Type
/dev/sda1 * 64 1024063 1024000 500M fd Linux raid autodetect
/dev/sda2 1024064 4294961684 4293937621 2T fd Linux raid autodetect
/dev/sda3 4294963200 7814035455 3519072256 1.6T fd Linux raid autodetect
sdb:
Device Boot Start End Sectors Size Id Type
/dev/sdb1 * 2048 1026047 1024000 500M fd Linux raid autodetect
/dev/sdb2 1026048 4294961684 4293935637 2T fd Linux raid autodetect
/dev/sdb3 4294963200 7814035455 3519072256 1.6T fd Linux raid autodetect
So ... on sda I could delete partition 1 so that it starts at 2048, but there
is not enough room as the start of partition 2 is closer to the start of disk,
so I would need to make it smaller on sdb as well.
Maybe I could mark sda1 and sda2 as failed, remove from raid, delete the
partitions & recreate as on sdb and let the mirror s/ware rebuild.
You may recall the note at the end of my original email ...
> Another problem is that it is 500 MB, trixie recommends that it should be 768
> MB; a problem that I shall worry about another day.
So: reduce the size of /dev/md1 by 1GB which would let me increase md0 (/boot)
by 1GB -- plenty of room for growth requirement of /boot in years to come.
I will sleep on it - do it with a fresh mind once I have had some coffee
tomorrow.
I must regard the system as unbootable until I fix this, although I could
prolly boot off sdb.
Regards
PS: you might wonder why I have partition 2 & partition 3.
It is a 4TB disk. DOS partitions can be max 2TB and max offset of 2TB. So I
created partitions 2 & 3 for md1 and md2 and put into the same volume group.
--
Alain Williams
Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256 https://www.phcomp.co.uk/
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