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/ Parliament Hill Computers. Registration Information: https://www.phcomp.co.uk/Contact.html #include <std_disclaimer.h>
