Resize the RAID1 root partition without rebooting

Resizing the root partition on a server 12 miles away seemed a bit risky. The root partition is on a software RAID1 mirror, no LVM. Twelve years ago I left only 2 GB for the root partition. I wanted to upgrade to Ubuntu 20.04.5 and the small size quickly became a problem. I managed to upgrade to Ubuntu 18.04.6 LTS, but ran out of space while upgrading to 20.04.5 LTS. Even after uninstalling previous versions, there was not enough space left. I had to make the root partition bigger. There was a relatively large 8 GB swap partition right after the root partition. The RAM is only 2 GB, so I was able to reduce the size of the swap. The plan was to delete the swap and extend the root partition, then create a smaller swapfile. I’ll show you how I did it. The server did not have to be restarted even once during the partition conversion. Finally, I have 5 GB free space after upgrading to Ubuntu 20.04.5 LTS.

Step 1. Identify the swap array (command ‘lsblk’).

In summary, I had to delete the md1 array and sda2+sdb2 partitions, then I had to increase the sda1+sdb2 partitions and the md0 array.

Step 2. Turn off the swap and delete it from /etc/fstab

Step 3. Remove the swap array and erase the RAID information. But before using mdadm, remove the swap entry from /etc/mdadm/mdadm.cfg. The line which starts with “ARRAY /dev/md/1” in my case. At least, I couldn’t stop the array without this.

Step 4. Delete the swap partitions from both disks then resize the root partition. I had to repeat this process for /dev/sdb. The value of End should match the value of the deleted swap partition. In my case it was 9999MB.

Step 5. Issue the ‘partprobe’ command to inform the OS of the partition table changes.

Step 6. Resize the RAID array. To calculate the new size, the partition size is a bit misleading. It seems to be about 10 GB, but if you look back at the output of the lsblk command it’s just 9.4 GB (1.9 GB + 7.5 GB). I was in a hurry, I didn’t have time to calculate the exact size, so I left it at 9400 MB.

Step 7. Resize the filesystem to match the new array size.

Step 8. Create a new swap file on the root partition and activate it.

Don’t forget to insert a line in /etc/fstab for the new swap image.

Step 9. Update grub and initramfs. Apt always gave an error message complaining about “no swap device available” when calling initramfs. I had a resume file in /etc/initramfs-tools/conf.d/ which is for hibernation. This file pointed to the old non-existent swap partition. I don’t use it for the server so I simply deleted it.

That’s all about it. No need to reboot the server.