One thing to be aware of is that R80.20 for management installations introduced the XFS filesystem, which is heavily recommended for management installations. The only way to get this new filesystem is by doing a clean installation. I'm not sure how you did your R80.40 installation, but I would recommend you to run "df -hT" via SSH to verify if you have XFS already or not:
[Expert@fwlog01:0]# df -T
Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_splat-lv_current xfs 26201600 8528584 17673016 33% /
/dev/sda2 ext3 297485 27115 255010 10% /boot
/dev/sda1 vfat 61302 7348 53954 12% /boot/efi
/dev/mapper/vg_splat-lv_log xfs 36684800 1993744 34691056 6% /var/log
tmpfs tmpfs 8089272 3876 8085396 1% /dev/shm
cgroup tmpfs 8089272 0 8089272 0% /sys/fs/cgroup
If you don't have the XFS filesystem already, I would recommend you to install R81.10 on a new host and migrate your installation to the new host instead of doing an in-place upgrade.
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