I've always been a fan of Ubuntu Server for my various services. I've been using it for years, and never really considered anything else, as I'm used to the Debian-like ecosystem.
I ran a lot of virtual machines, all using a base Ubuntu image that I had customized. I ended up playing with a service that required installation on top of Debian 10. The installation surprised me, as it was fairly quick, and the VM booted almost instantly. Then Debian 11 dropped, and I decided to convert one of my heftier VMs over to it. Boot time alone for the VM was impressive. I eventually converted all my VMs to Debian 11.
I also run a pretty beefy NAS box. Dual bonded NICs, Xeon processor, 32Gb RAM, and around 30Tb ZFS storage, also running on Ubuntu. The OS is installed on an NVME SSD. I run a few docker containers, the primary service being Emby. I initially decided not to convert it to Debian due to the pain of getting it back up and running as I like it, but it nagged on my mind for a long time, and yesterday, I bit the bullet.
I moved all my VM disks off the NAS to alternate locations so that my VMs didn't have to be offline for the reinstall. I backed up all the important stuff and ensured there was an offline copy of that backup in case things went horribly wrong. I shut down the containers, disabled all the sharing, then exported the ZFS pools and shut down the machine.
While the machine was down, I took the opportunity to install a quad NIC that I intend to use for storage motion between my two VM hypervisors. I'm just waiting for the two brackets I ordered to arrive before I install the dual NICs into the two hypervisors.
I installed Debian 11. The actual installation was surprisingly quick, and the initial boot time was astounding. It took literally less than a second from Grub to login prompt. Ubuntu took considerably longer to boot.
I set up the bonded NICs via systemd-network, added the necessary repositories to install ZFS, then imported the pools. Getting Samba and NFS up and running was a matter of copying my old configs across and starting the services, and extracting the backups of my containers, and then starting them up.
The ZFS installation affected the boot time very slightly. Instead of taking less than a second, it now takes less than 2 seconds, or thereabouts. Still far superior to Ubuntu.
Starting playback via Emby is a lot faster, and I noticed a definite and considerable improvement in network performance when copying large files from one of my VMs via NFS. The network performance has improved by around 50%. I always thought the performance was affected by the data coming from a VM that has to contend with other VMs using the hypervisor NIC, and it being NFS. Turns out that's not entirely the case!
Ultimately I'm very impressed at the quite noticeable improvements in performance I'm seeing between Ubuntu and Debian, and it's not just me. I helped someone else convert from Ubuntu to Debian, and the improvement was noticeable, even on older hardware.